diff --git a/core/nwb.base.yaml b/core/nwb.base.yaml
index f926cab3..4562547c 100644
--- a/core/nwb.base.yaml
+++ b/core/nwb.base.yaml
@@ -128,8 +128,8 @@ groups:
       doc: Sampling rate, in Hz.
     - name: unit
       dtype: text
-      value: seconds
-      doc: Unit of measurement for time, which is fixed to 'seconds'.
+      value: s
+      doc: Unit of measurement for time, which is fixed to 's'.
   - name: timestamps
     dtype: float64
     dims:
@@ -146,8 +146,8 @@ groups:
       doc: Value is '1'
     - name: unit
       dtype: text
-      value: seconds
-      doc: Unit of measurement for timestamps, which is fixed to 'seconds'.
+      value: s
+      doc: Unit of measurement for timestamps, which is fixed to 's'.
   - name: control
     dtype: uint8
     dims:
diff --git a/core/nwb.behavior.yaml b/core/nwb.behavior.yaml
index 300b48db..cb3fa725 100644
--- a/core/nwb.behavior.yaml
+++ b/core/nwb.behavior.yaml
@@ -25,9 +25,9 @@ groups:
     attributes:
     - name: unit
       dtype: text
-      default_value: meters
+      default_value: m
       doc: Base unit of measurement for working with the data. The default value
-        is 'meters'. Actual stored values are not necessarily stored in these units.
+        is 'm'. Actual stored values are not necessarily stored in these units.
         To access the data in these units, multiply 'data' by 'conversion'.
       required: false
   - name: reference_frame
diff --git a/core/nwb.ecephys.yaml b/core/nwb.ecephys.yaml
index 90c8655d..f33647ab 100644
--- a/core/nwb.ecephys.yaml
+++ b/core/nwb.ecephys.yaml
@@ -26,9 +26,9 @@ groups:
     attributes:
     - name: unit
       dtype: text
-      value: volts
+      value: V
       doc: Base unit of measurement for working with the data. This value is fixed to
-        'volts'. Actual stored values are not necessarily stored in these units. To
+        'V'. Actual stored values are not necessarily stored in these units. To
         access the data in these units, multiply 'data' by 'conversion' and
         'channel_conversion' (if present).
   - name: electrodes
@@ -84,8 +84,8 @@ groups:
     attributes:
     - name: unit
       dtype: text
-      value: volts
-      doc: Unit of measurement for waveforms, which is fixed to 'volts'.
+      value: V
+      doc: Unit of measurement for waveforms, which is fixed to 'V'.
   - name: timestamps
     dtype: float64
     dims:
@@ -103,8 +103,8 @@ groups:
       doc: Value is '1'
     - name: unit
       dtype: text
-      value: seconds
-      doc: Unit of measurement for timestamps, which is fixed to 'seconds'.
+      value: s
+      doc: Unit of measurement for timestamps, which is fixed to 's'.
 
 - neurodata_type_def: FeatureExtraction
   neurodata_type_inc: NWBDataInterface
@@ -170,8 +170,8 @@ groups:
     attributes:
     - name: unit
       dtype: text
-      value: seconds
-      doc: Unit of measurement for event times, which is fixed to 'seconds'.
+      value: s
+      doc: Unit of measurement for event times, which is fixed to 's'.
   links:
   - name: source_electricalseries
     target_type: ElectricalSeries
diff --git a/core/nwb.file.yaml b/core/nwb.file.yaml
index 2376f36d..6cb6acc0 100644
--- a/core/nwb.file.yaml
+++ b/core/nwb.file.yaml
@@ -7,7 +7,7 @@ groups:
   attributes:
   - name: nwb_version
     dtype: text
-    value: 2.2.5
+    value: 2.3.0-alpha
     doc: File version string. Use semantic versioning, e.g. 1.2.1. This will be the
       name of the format with trailing major, minor and patch numbers.
   datasets:
diff --git a/core/nwb.icephys.yaml b/core/nwb.icephys.yaml
index a3065166..06dc8c85 100644
--- a/core/nwb.icephys.yaml
+++ b/core/nwb.icephys.yaml
@@ -46,22 +46,37 @@ groups:
     attributes:
     - name: unit
       dtype: text
-      value: volts
-      doc: Base unit of measurement for working with the data. which is fixed to 'volts'.
+      value: V
+      doc: Base unit of measurement for working with the data. which is fixed to 'V'.
         Actual stored values are not necessarily stored in these units. To access the data in these units,
         multiply 'data' by 'conversion'.
   - name: bias_current
     dtype: float32
     doc: Bias current, in amps.
     quantity: '?'
+    attributes:
+    - name: unit
+      dtype: text
+      value: A
+      doc: Unit of measurement for bias_current, which is fixed to 'A'.
   - name: bridge_balance
     dtype: float32
     doc: Bridge balance, in ohms.
     quantity: '?'
+    attributes:
+    - name: unit
+      dtype: text
+      value: Ohm
+      doc: Unit of measurement for bridge_balance, which is fixed to 'Ohm'.
   - name: capacitance_compensation
     dtype: float32
     doc: Capacitance compensation, in farads.
     quantity: '?'
+    attributes:
+    - name: unit
+      dtype: text
+      value: F
+      doc: Unit of measurement for capacitance_compensation, which is fixed to 'F'.
 
 - neurodata_type_def: IZeroClampSeries
   neurodata_type_inc: CurrentClampSeries
@@ -92,8 +107,8 @@ groups:
     attributes:
     - name: unit
       dtype: text
-      value: amperes
-      doc: Base unit of measurement for working with the data. which is fixed to 'amperes'.
+      value: A
+      doc: Base unit of measurement for working with the data. which is fixed to 'A'.
         Actual stored values are not necessarily stored in these units. To access the data in these units,
         multiply 'data' by 'conversion'.
 
@@ -108,8 +123,8 @@ groups:
     attributes:
     - name: unit
       dtype: text
-      value: amperes
-      doc: Base unit of measurement for working with the data. which is fixed to 'amperes'.
+      value: A
+      doc: Base unit of measurement for working with the data. which is fixed to 'A'.
         Actual stored values are not necessarily stored in these units. To access the data in these units,
         multiply 'data' by 'conversion'.
   - name: capacitance_fast
@@ -119,8 +134,8 @@ groups:
     attributes:
     - name: unit
       dtype: text
-      value: farads
-      doc: Unit of measurement for capacitance_fast, which is fixed to 'farads'.
+      value: F
+      doc: Unit of measurement for capacitance_fast, which is fixed to 'F'.
   - name: capacitance_slow
     dtype: float32
     doc: Slow capacitance, in farads.
@@ -128,8 +143,8 @@ groups:
     attributes:
     - name: unit
       dtype: text
-      value: farads
-      doc: Unit of measurement for capacitance_fast, which is fixed to 'farads'.
+      value: F
+      doc: Unit of measurement for capacitance_fast, which is fixed to 'F'.
   - name: resistance_comp_bandwidth
     dtype: float32
     doc: Resistance compensation bandwidth, in hertz.
@@ -137,8 +152,8 @@ groups:
     attributes:
     - name: unit
       dtype: text
-      value: hertz
-      doc: Unit of measurement for resistance_comp_bandwidth, which is fixed to 'hertz'.
+      value: Hz
+      doc: Unit of measurement for resistance_comp_bandwidth, which is fixed to 'Hz'.
   - name: resistance_comp_correction
     dtype: float32
     doc: Resistance compensation correction, in percent.
@@ -146,8 +161,8 @@ groups:
     attributes:
     - name: unit
       dtype: text
-      value: percent
-      doc: Unit of measurement for resistance_comp_correction, which is fixed to 'percent'.
+      value: '%'
+      doc: Unit of measurement for resistance_comp_correction, which is fixed to '%'.
   - name: resistance_comp_prediction
     dtype: float32
     doc: Resistance compensation prediction, in percent.
@@ -155,8 +170,8 @@ groups:
     attributes:
     - name: unit
       dtype: text
-      value: percent
-      doc: Unit of measurement for resistance_comp_prediction, which is fixed to 'percent'.
+      value: '%'
+      doc: Unit of measurement for resistance_comp_prediction, which is fixed to '%'.
   - name: whole_cell_capacitance_comp
     dtype: float32
     doc: Whole cell capacitance compensation, in farads.
@@ -164,8 +179,8 @@ groups:
     attributes:
     - name: unit
       dtype: text
-      value: farads
-      doc: Unit of measurement for whole_cell_capacitance_comp, which is fixed to 'farads'.
+      value: F
+      doc: Unit of measurement for whole_cell_capacitance_comp, which is fixed to 'F'.
   - name: whole_cell_series_resistance_comp
     dtype: float32
     doc: Whole cell series resistance compensation, in ohms.
@@ -173,8 +188,8 @@ groups:
     attributes:
     - name: unit
       dtype: text
-      value: ohms
-      doc: Unit of measurement for whole_cell_series_resistance_comp, which is fixed to 'ohms'.
+      value: Ohm
+      doc: Unit of measurement for whole_cell_series_resistance_comp, which is fixed to 'Ohm'.
 
 - neurodata_type_def: VoltageClampStimulusSeries
   neurodata_type_inc: PatchClampSeries
@@ -185,8 +200,8 @@ groups:
     attributes:
     - name: unit
       dtype: text
-      value: volts
-      doc: Base unit of measurement for working with the data. which is fixed to 'volts'.
+      value: V
+      doc: Base unit of measurement for working with the data. which is fixed to 'V'.
         Actual stored values are not necessarily stored in these units. To access the data in these units,
         multiply 'data' by 'conversion'.
 
diff --git a/core/nwb.misc.yaml b/core/nwb.misc.yaml
index c8723ba3..1fea6119 100644
--- a/core/nwb.misc.yaml
+++ b/core/nwb.misc.yaml
@@ -25,9 +25,9 @@ groups:
     attributes:
     - name: unit
       dtype: text
-      default_value: see 'feature_units'
+      default_value: n/a
       doc: Since there can be different units for different features, store the units
-        in 'feature_units'. The default value for this attribute is "see 'feature_units'".
+        in 'feature_units'. The default value for this attribute is "n/a".
       required: false
   - name: feature_units
     dtype: text
@@ -35,7 +35,7 @@ groups:
     - num_features
     shape:
     - null
-    doc: Units of each feature.
+    doc: Units of measurement of each feature.
     quantity: '?'
   - name: features
     dtype: text
@@ -115,13 +115,6 @@ groups:
     - null
     - null
     doc: Data decomposed into frequency bands.
-    attributes:
-    - name: unit
-      dtype: text
-      default_value: no unit
-      doc: Base unit of measurement for working with the data. Actual stored values are
-        not necessarily stored in these units. To access the data in these units,
-        multiply 'data' by 'conversion'.
   - name: metric
     dtype: text
     doc: The metric used, e.g. phase, amplitude, power.
@@ -247,8 +240,8 @@ groups:
       required: false
     - name: unit
       dtype: text
-      value: volts
-      doc: Unit of measurement. This value is fixed to 'volts'.
+      value: V
+      doc: Unit of measurement. This value is fixed to 'V'.
       required: false
   - name: waveform_sd
     neurodata_type_inc: VectorData
@@ -274,6 +267,6 @@ groups:
       required: false
     - name: unit
       dtype: text
-      value: volts
-      doc: Unit of measurement. This value is fixed to 'volts'.
+      value: V
+      doc: Unit of measurement. This value is fixed to 'V'.
       required: false
diff --git a/core/nwb.namespace.yaml b/core/nwb.namespace.yaml
index c3ec78ad..c0d1225e 100644
--- a/core/nwb.namespace.yaml
+++ b/core/nwb.namespace.yaml
@@ -57,4 +57,4 @@ namespaces:
   - doc: This source module contains neurodata_type for retinotopy data.
     source: nwb.retinotopy.yaml
     title: Retinotopy
-  version: 2.2.5
+  version: 2.3.0-alpha
diff --git a/core/nwb.ogen.yaml b/core/nwb.ogen.yaml
index 1756ba85..d0f6cecf 100644
--- a/core/nwb.ogen.yaml
+++ b/core/nwb.ogen.yaml
@@ -13,8 +13,8 @@ groups:
     attributes:
     - name: unit
       dtype: text
-      value: watts
-      doc: Unit of measurement for data, which is fixed to 'watts'.
+      value: W
+      doc: Unit of measurement for data, which is fixed to 'W'.
   links:
   - name: site
     target_type: OptogeneticStimulusSite
diff --git a/core/nwb.ophys.yaml b/core/nwb.ophys.yaml
index 386dca9b..50d9f22a 100644
--- a/core/nwb.ophys.yaml
+++ b/core/nwb.ophys.yaml
@@ -226,8 +226,8 @@ groups:
       required: false
     - name: unit
       dtype: text
-      default_value: meters
-      doc: Base unit of measurement for working with the data. The default value is 'meters'.
+      default_value: m
+      doc: Base unit of measurement for working with the data. The default value is 'm'.
       required: false
   - name: origin_coords
     dtype: float32
@@ -243,8 +243,8 @@ groups:
     attributes:
     - name: unit
       dtype: text
-      default_value: meters
-      doc: Measurement units for origin_coords. The default value is 'meters'.
+      default_value: m
+      doc: Measurement units for origin_coords. The default value is 'm'.
   - name: grid_spacing
     dtype: float32
     dims:
@@ -259,8 +259,8 @@ groups:
     attributes:
     - name: unit
       dtype: text
-      default_value: meters
-      doc: Measurement units for grid_spacing. The default value is 'meters'.
+      default_value: m
+      doc: Measurement units for grid_spacing. The default value is 'm'.
   - name: reference_frame
     dtype: text
     doc: Describes reference frame of origin_coords and grid_spacing.
diff --git a/core/nwb.retinotopy.yaml b/core/nwb.retinotopy.yaml
index e8972395..117af491 100644
--- a/core/nwb.retinotopy.yaml
+++ b/core/nwb.retinotopy.yaml
@@ -39,7 +39,7 @@ groups:
       doc: Size of viewing area, in meters.
     - name: unit
       dtype: text
-      doc: Unit that axis data is stored in (e.g., degrees).
+      doc: Unit of measurement for axis data, e.g., "o" for degrees.
   - name: axis_1_power_map
     dtype: float32
     dims:
@@ -69,7 +69,7 @@ groups:
       doc: Size of viewing area, in meters.
     - name: unit
       dtype: text
-      doc: Unit that axis data is stored in (e.g., degrees).
+      doc: Unit of measurement for axis data, e.g., "o" for degrees.
   - name: axis_2_phase_map
     dtype: float32
     dims:
@@ -97,7 +97,7 @@ groups:
       doc: Size of viewing area, in meters.
     - name: unit
       dtype: text
-      doc: Unit that axis data is stored in (e.g., degrees).
+      doc: Unit of measurement for axis data, e.g., "o" for degrees.
   - name: axis_2_power_map
     dtype: float32
     dims:
@@ -127,7 +127,7 @@ groups:
       doc: Size of viewing area, in meters.
     - name: unit
       dtype: text
-      doc: Unit that axis data is stored in (e.g., degrees).
+      doc: Unit of measurement for axis data, e.g., "o" for degrees.
   - name: axis_descriptions
     dtype: text
     dims:
diff --git a/docs/format/source/conf.py b/docs/format/source/conf.py
index 30d39668..23f8f87e 100644
--- a/docs/format/source/conf.py
+++ b/docs/format/source/conf.py
@@ -83,7 +83,7 @@ def setup(app):
 # built documents.
 #
 # The short X.Y version.
-version = 'v2.2.5'
+version = 'v2.3.0-alpha'
 # The full version, including alpha/beta/rc tags.
 release = version
 
diff --git a/docs/format/source/format_description.rst b/docs/format/source/format_description.rst
index b6bc4303..5203c0ad 100644
--- a/docs/format/source/format_description.rst
+++ b/docs/format/source/format_description.rst
@@ -274,6 +274,112 @@ For fields with a specified size, larger sizes can be used, so long as
 the selected size encompasses the full range of data, and for floats,
 without loss of significant precision.
 
+Units of Measurement
+--------------------
+
+As of NWB 2.3.0, the specification of units of measurement SHOULD follow the
+`International System of Units (SI)`_ and SHOULD be formatted using
+the `CMIXF-12 format`_. CMIXF provides a consistent system for all units and
+prefix symbols with only basic characters, avoiding symbols that can cause
+text encoding problems; for example, the CMIXF formatting for "microvolts"
+is "uV", "degrees Celsius" is "oC", and "Ohm" is "Ohm".
+
+Units MUST consist of the unit symbol with an optionally accompanying
+prefix symbol. Appropriate upper- or lower-casing MUST be applied as declared
+by CMIXF-12.
+
+Common units in neurophysiology and their symbols:
+
++-------------------+-------------+----------------------------------+
+| Unit name         | Unit symbol | Quantity name                    |
++===================+=============+==================================+
+| second            | s           | time                             |
++-------------------+-------------+----------------------------------+
+| volt              | V           | voltage                          |
++-------------------+-------------+----------------------------------+
+| meter (metre)     | m           | length                           |
++-------------------+-------------+----------------------------------+
+| hertz             | Hz          | frequency                        |
++-------------------+-------------+----------------------------------+
+| ampere            | A           | electric current                 |
++-------------------+-------------+----------------------------------+
+| ohm               | Ohm         | electric resistance, impedance   |
++-------------------+-------------+----------------------------------+
+| farad             | F           | capcaitance                      |
++-------------------+-------------+----------------------------------+
+| watt              | W           | power                            |
++-------------------+-------------+----------------------------------+
+| joule             | J           | energy, heat                     |
++-------------------+-------------+----------------------------------+
+| percent           | %           | part of 100                      |
++-------------------+-------------+----------------------------------+
+| degree            | o           | plane angle                      |
++-------------------+-------------+----------------------------------+
+| radian            | r           | plane angle                      |
++-------------------+-------------+----------------------------------+
+| decibel           | dB          | logarithm of power ratio         |
++-------------------+-------------+----------------------------------+
+| gram              | g           | mass                             |
++-------------------+-------------+----------------------------------+
+| liter (litre)     | L           | volume                           |
++-------------------+-------------+----------------------------------+
+| mole              | mol         | amount of substance              |
++-------------------+-------------+----------------------------------+
+| degree Celsius    | oC          | temperature relative to 273.15 K |
++-------------------+-------------+----------------------------------+
+
+Common prefixes:
+
++-------------+---------------+--------+
+| Prefix name | Prefix symbol | Factor |
++=============+===============+========+
+| giga        | G             | 10^9   |
++-------------+---------------+--------+
+| mega        | M             | 10^6   |
++-------------+---------------+--------+
+| kilo        | k             | 10^3   |
++-------------+---------------+--------+
+| centi       | c             | 10^-2  |
++-------------+---------------+--------+
+| milli       | m             | 10^-3  |
++-------------+---------------+--------+
+| micro       | u             | 10^-6  |
++-------------+---------------+--------+
+| nano        | n             | 10^-9  |
++-------------+---------------+--------+
+| pico        | p             | 10^-12 |
++-------------+---------------+--------+
+
+Exceptions to the above formatting:
+
+- Arbitrary units should be represented as "a.u.".
+- Unit-less data should be represented as "n/a".
+- "pixel" may be used for measurements of image data.
+- "voxel" may be used for measurements of volume data.
+
+The unit of measurement for a value is most commonly stored in the "unit"
+attribute to a dataset, e.g., ``TimeSeries.data..unit``. If the dataset
+has no "unit" attribute, consult the docstring for the dataset, which
+may specify a unit. Note that attributes cannot have nested attributes,
+so all attributes must specify their unit in the docstring. For this
+reason, it is recommended that all data and metadata with units be stored
+as datasets rather than attributes. NWB extensions should also use the
+format and guidance specified in this section.
+
+This specification follows the adoption of CMIXF-12 by BIDS (TODO include
+link).
+
+Age values of subjects SHOULD be given in `ISO8601 duration format`_ and
+it is RECOMMENDED that the age is provided at the highest resolution
+available, except when a high resolution should be avoided due to privacy
+protection, e.g., of human subjects. For example, the age of a mouse that
+is 50 days old should be represented as "P50D". For different types of age
+(e.g., days post-fertilization), use the "age_reference" attribute.
+
+.. _`International System of Units (SI)`: https://en.wikipedia.org/wiki/International_System_of_Units
+.. _`CMIXF-12 format`: http://people.csail.mit.edu/jaffer/MIXF/CMIXF-12
+.. _`ISO8601 duration format`: https://en.wikipedia.org/wiki/ISO_8601#Durations
+
 Links and data references
 -------------------------
 
diff --git a/docs/format/source/format_release_notes.rst b/docs/format/source/format_release_notes.rst
index 8d54affc..c57d27d2 100644
--- a/docs/format/source/format_release_notes.rst
+++ b/docs/format/source/format_release_notes.rst
@@ -1,6 +1,12 @@
 Release Notes
 =============
 
+2.3.0 (Upcoming)
+----------------------
+
+- All "unit" fields representing units of measurement now follow the CMIXF-12 format as described in:
+  https://nwb-schema.readthedocs.io/en/latest/format_description.html#units-of-measurement
+
 2.2.5 (May 29, 2020)
 ----------------------