diff --git a/CHANGELOG.md b/CHANGELOG.md
index 822b0af31..fcf237af7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -29,6 +29,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * `playwright.controller.InputActionButton` gains a `expect_icon()` method. As a result, the already existing `expect_label()` no longer includes the icon. (#2020)
 
+* `ui.sidebar()` gains a `fillable` argument to support vertical fill behavior in sidebars. (#2077)
+
 ### Changes
 
 * `express.ui.insert_accordion_panel()`'s function signature has changed to be more ergonomic. Now you can pass the `panel_title` and `panel_contents` directly instead of `ui.hold()`ing the `ui.accordion_panel()` context manager. (#2042)
diff --git a/shiny/express/ui/_cm_components.py b/shiny/express/ui/_cm_components.py
index 651d61620..3f9f14dab 100644
--- a/shiny/express/ui/_cm_components.py
+++ b/shiny/express/ui/_cm_components.py
@@ -64,6 +64,7 @@ def sidebar(
     max_height_mobile: Optional[str | float] = None,
     gap: Optional[CssUnit] = None,
     padding: Optional[CssUnit | list[CssUnit]] = None,
+    fillable: bool = False,
     **kwargs: TagAttrValue,
 ) -> RecallContextManager[ui.Sidebar]:
     """
@@ -122,6 +123,10 @@ def sidebar(
           and right, and the third will be bottom.
         * If four, then the values will be interpreted as top, right, bottom, and left
           respectively.
+    fillable
+        Whether or not the sidebar should be considered a fillable container.
+        When `True`, the sidebar and its content can use `fill` to consume
+        available vertical space.
     **kwargs
         Named attributes are supplied to the sidebar content container.
     """
@@ -139,6 +144,7 @@ def sidebar(
             max_height_mobile=max_height_mobile,
             gap=gap,
             padding=padding,
+            fillable=fillable,
             **kwargs,
         ),
     )
diff --git a/shiny/ui/_sidebar.py b/shiny/ui/_sidebar.py
index a17d1957b..eb442434f 100644
--- a/shiny/ui/_sidebar.py
+++ b/shiny/ui/_sidebar.py
@@ -206,6 +206,10 @@ class directly. Instead, supply the :func:`~shiny.ui.sidebar` object to
           and right, and the third will be bottom.
         * If four, then the values will be interpreted as top, right, bottom, and left
           respectively.
+    fillable
+        Whether or not the sidebar should be considered a fillable container.
+        When `True`, the sidebar and its content can use `fill` to consume
+        available vertical space.
 
     Parameters
     ----------
@@ -283,6 +287,7 @@ def __init__(
         max_height_mobile: Optional[str | float] = None,
         gap: Optional[CssUnit] = None,
         padding: Optional[CssUnit | list[CssUnit]] = None,
+        fillable: bool = False,
     ):
         if isinstance(title, (str, int, float)):
             title = tags.header(str(title), class_="sidebar-title")
@@ -292,6 +297,7 @@ def __init__(
         self.class_ = class_
         self.gap = as_css_unit(gap)
         self.padding = as_css_padding(padding)
+        self.fillable = fillable
         # User-provided initial open state
         self._open: SidebarOpen | None = self._as_open(open)
         # Shiny or consumer-provided default open state, change with `_set_default_open()`
@@ -403,7 +409,27 @@ def _sidebar_tag(self, id: str | None) -> Tag:
             self.open().desktop == "closed" or self.open().mobile == "closed"
         )
 
-        return tags.aside(
+        # Create the sidebar content div
+        sidebar_content = div(
+            {
+                "class": "sidebar-content bslib-gap-spacing",
+                "style": css(
+                    gap=self.gap,
+                    padding=self.padding,
+                ),
+            },
+            self.title,
+            *self.children,
+            self.attrs,
+        )
+
+        # Apply fill_item to the content div if fillable
+        if self.fillable:
+            sidebar_content = as_fill_item(sidebar_content)
+            sidebar_content = as_fillable_container(sidebar_content)
+
+        # Create the sidebar tag
+        sidebar_tag = tags.aside(
             {
                 "id": id,
                 "class": "sidebar",
@@ -411,21 +437,16 @@ def _sidebar_tag(self, id: str | None) -> Tag:
             },
             # If the user provided an id, we make the sidebar an input to report state
             {"class": "bslib-sidebar-input"} if self.id is not None else None,
-            div(
-                {
-                    "class": "sidebar-content bslib-gap-spacing",
-                    "style": css(
-                        gap=self.gap,
-                        padding=self.padding,
-                    ),
-                },
-                self.title,
-                *self.children,
-                self.attrs,
-            ),
+            sidebar_content,
             class_=self.class_,
         )
 
+        # Apply fillable container to the sidebar if needed
+        if self.fillable:
+            sidebar_tag = as_fillable_container(sidebar_tag)
+
+        return sidebar_tag
+
     def tagify(self) -> TagList:
         id = self._get_sidebar_id()
         taglist = TagList(self._sidebar_tag(id), self._collapse_tag(id))
@@ -446,6 +467,7 @@ def sidebar(
     max_height_mobile: Optional[str | float] = None,
     gap: Optional[CssUnit] = None,
     padding: Optional[CssUnit | list[CssUnit]] = None,
+    fillable: bool = False,
     **kwargs: TagAttrValue,
 ) -> Sidebar:
     # See [this article](https://rstudio.github.io/bslib/articles/sidebars.html)
@@ -521,6 +543,10 @@ def sidebar(
           and right, and the third will be bottom.
         * If four, then the values will be interpreted as top, right, bottom, and left
           respectively.
+    fillable
+        Whether or not the sidebar should be considered a fillable container.
+        When `True`, the sidebar and its content can use `fill` to consume
+        available vertical space.
     **kwargs
         Named attributes are supplied to the sidebar content container.
 
@@ -567,6 +593,7 @@ def sidebar(
         max_height_mobile=max_height_mobile,
         gap=gap,
         padding=padding,
+        fillable=fillable,
     )