diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0e76074..d0b828d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@
 - Added `logging.LoggerAdapter` to `_MaybeLogger` union https://github.com/python-backoff/backoff/pull/34 (from @jcbertin)
 - Add `exception` to the typing-only `Details` dictionary for cases when `on_exception` is used https://github.com/python-backoff/backoff/pull/35 (from @edgarrmondragon)
 - Add GitHub Actions for CI, documentation, and publishing https://github.com/python-backoff/backoff/pull/39 (from @tysoncung)
+- Use `time.monotonic` instead of `datetime.datetime.now` https://github.com/python-backoff/backoff/pull/23 (from @luccabb)
 
 ### Packaging
 
diff --git a/backoff/_async.py b/backoff/_async.py
index b9e8d3e..7c950b2 100644
--- a/backoff/_async.py
+++ b/backoff/_async.py
@@ -1,11 +1,10 @@
 # coding:utf-8
-import datetime
-import functools
 import asyncio
+import functools
 import inspect
-from datetime import timedelta
+import time
 
-from backoff._common import (_init_wait_gen, _maybe_call, _next_wait)
+from backoff._common import _init_wait_gen, _maybe_call, _next_wait
 
 
 def _ensure_coroutine(coro_or_func):
@@ -61,11 +60,11 @@ async def retry(*args, **kwargs):
         max_time_value = _maybe_call(max_time)
 
         tries = 0
-        start = datetime.datetime.now()
+        start = time.monotonic()
         wait = _init_wait_gen(wait_gen, wait_gen_kwargs)
         while True:
             tries += 1
-            elapsed = timedelta.total_seconds(datetime.datetime.now() - start)
+            elapsed = time.monotonic() - start
             details = {
                 "target": target,
                 "args": args,
@@ -135,11 +134,11 @@ async def retry(*args, **kwargs):
         max_time_value = _maybe_call(max_time)
 
         tries = 0
-        start = datetime.datetime.now()
+        start = time.monotonic()
         wait = _init_wait_gen(wait_gen, wait_gen_kwargs)
         while True:
             tries += 1
-            elapsed = timedelta.total_seconds(datetime.datetime.now() - start)
+            elapsed = time.monotonic() - start
             details = {
                 "target": target,
                 "args": args,
diff --git a/backoff/_sync.py b/backoff/_sync.py
index 4371e16..d8d0046 100644
--- a/backoff/_sync.py
+++ b/backoff/_sync.py
@@ -1,8 +1,6 @@
 # coding:utf-8
-import datetime
 import functools
 import time
-from datetime import timedelta
 
 from backoff._common import (_init_wait_gen, _maybe_call, _next_wait)
 
@@ -32,11 +30,11 @@ def retry(*args, **kwargs):
         max_time_value = _maybe_call(max_time)
 
         tries = 0
-        start = datetime.datetime.now()
+        start = time.monotonic()
         wait = _init_wait_gen(wait_gen, wait_gen_kwargs)
         while True:
             tries += 1
-            elapsed = timedelta.total_seconds(datetime.datetime.now() - start)
+            elapsed = time.monotonic() - start
             details = {
                 "target": target,
                 "args": args,
@@ -88,11 +86,11 @@ def retry(*args, **kwargs):
         max_time_value = _maybe_call(max_time)
 
         tries = 0
-        start = datetime.datetime.now()
+        start = time.monotonic()
         wait = _init_wait_gen(wait_gen, wait_gen_kwargs)
         while True:
             tries += 1
-            elapsed = timedelta.total_seconds(datetime.datetime.now() - start)
+            elapsed = time.monotonic() - start
             details = {
                 "target": target,
                 "args": args,
diff --git a/tests/test_backoff.py b/tests/test_backoff.py
index 800756a..7d46269 100644
--- a/tests/test_backoff.py
+++ b/tests/test_backoff.py
@@ -1,5 +1,4 @@
 # coding:utf-8
-import datetime
 import itertools
 import logging
 import random
@@ -47,19 +46,17 @@ def return_true(log, n):
 
 def test_on_predicate_max_time(monkeypatch):
     nows = [
-        datetime.datetime(2018, 1, 1, 12, 0, 10, 5),
-        datetime.datetime(2018, 1, 1, 12, 0, 9, 0),
-        datetime.datetime(2018, 1, 1, 12, 0, 1, 0),
-        datetime.datetime(2018, 1, 1, 12, 0, 0, 0),
+        10.000005,
+        9,
+        1,
+        0
     ]
 
-    class Datetime:
-        @staticmethod
-        def now():
-            return nows.pop()
+    def monotonic():
+        return nows.pop()
 
     monkeypatch.setattr('time.sleep', lambda x: None)
-    monkeypatch.setattr('datetime.datetime', Datetime)
+    monkeypatch.setattr('time.monotonic', monotonic)
 
     def giveup(details):
         assert details['tries'] == 3
@@ -80,19 +77,17 @@ def return_true(log, n):
 
 def test_on_predicate_max_time_callable(monkeypatch):
     nows = [
-        datetime.datetime(2018, 1, 1, 12, 0, 10, 5),
-        datetime.datetime(2018, 1, 1, 12, 0, 9, 0),
-        datetime.datetime(2018, 1, 1, 12, 0, 1, 0),
-        datetime.datetime(2018, 1, 1, 12, 0, 0, 0),
+        10.000005,
+        9,
+        1,
+        0
     ]
 
-    class Datetime:
-        @staticmethod
-        def now():
-            return nows.pop()
+    def monotonic():
+        return nows.pop()
 
     monkeypatch.setattr('time.sleep', lambda x: None)
-    monkeypatch.setattr('datetime.datetime', Datetime)
+    monkeypatch.setattr('time.monotonic', monotonic)
 
     def giveup(details):
         assert details['tries'] == 3
@@ -502,7 +497,6 @@ def emptiness(*args, **kwargs):
         assert len(logger.giveups) == 1
 
         details = dict(logger.giveups[0])
-        print(details)
         elapsed = details.pop('elapsed')
         assert isinstance(elapsed, float)
         assert details == {'args': (1, 2, 3),
@@ -591,7 +585,6 @@ def success(*args, **kwargs):
 
     for i in range(2):
         details = backoffs[i]
-        print(details)
         elapsed = details.pop('elapsed')
         assert isinstance(elapsed, float)
         assert details == {'args': (1, 2, 3),