diff --git a/app/assets/stylesheets/base/root.css b/app/assets/stylesheets/base/root.css
index 9324f4a..10d4984 100644
--- a/app/assets/stylesheets/base/root.css
+++ b/app/assets/stylesheets/base/root.css
@@ -6,9 +6,9 @@ body {
 }
 
 .container {
-  max-width: var(--max-width-container);
+  max-width: none;
   width: 100%;
-  margin: 0 auto;
+  margin: 0;
   padding: 0;
   background-color: var(--color-bg-container);
   min-width: 0;
@@ -16,16 +16,66 @@ body {
 }
 
 .page-layout.with-sidebar {
+  --sidebar-width: 360px;
+  --sidebar-resizer-width: 10px;
   display: grid;
-  grid-template-columns: 480px 1fr;
+  grid-template-columns: var(--sidebar-width) var(--sidebar-resizer-width) minmax(0, 1fr);
+  grid-template-areas: "sidebar resizer main";
   gap: 0;
   align-items: start;
+  overflow: visible;
 }
 
 .page-layout.with-sidebar .layout-sidebar {
   background: var(--color-bg-card);
-  border-right: var(--border-width) solid var(--color-border);
   min-height: calc(100vh - var(--nav-height));
   background-color: var(--color-bg-sidebar);
   align-self: stretch;
+  min-width: 0;
+  grid-area: sidebar;
+}
+
+.page-layout.with-sidebar .layout-sidebar-resizer {
+  cursor: col-resize;
+  background: var(--color-bg-page);
+  border-right: var(--border-width) solid var(--color-border);
+  min-height: calc(100vh - var(--nav-height));
+  position: sticky;
+  top: var(--nav-height);
+  touch-action: none;
+  width: var(--sidebar-resizer-width);
+  grid-area: resizer;
+}
+
+.page-layout.with-sidebar .layout-sidebar-resizer:hover,
+.page-layout.with-sidebar .layout-sidebar-resizer:active {
+  background: var(--color-bg-hover);
+}
+
+body.sidebar-resizing {
+  cursor: col-resize;
+  user-select: none;
+}
+
+body.sidebar-collapsed .page-layout.with-sidebar {
+  grid-template-columns: 0 var(--sidebar-resizer-width) minmax(0, 1fr);
+}
+
+body.sidebar-collapsed .layout-sidebar {
+  visibility: hidden;
+  pointer-events: none;
+}
+
+body.sidebar-collapsed .layout-sidebar-resizer {
+  border-left: var(--border-width) solid var(--color-border);
+  justify-self: start;
+}
+
+body.sidebar-collapsed .page-layout.with-sidebar > main.container {
+  max-width: none;
+  width: 100%;
+}
+
+.page-layout.with-sidebar > main.container {
+  grid-area: main;
 }
diff --git a/app/assets/stylesheets/components/sidebar.css b/app/assets/stylesheets/components/sidebar.css
index 579c779..4ad74b6 100644
--- a/app/assets/stylesheets/components/sidebar.css
+++ b/app/assets/stylesheets/components/sidebar.css
@@ -7,6 +7,32 @@
   padding-right: var(--spacing-2);
 }
 
+.layout-sidebar-resizer {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+}
+
+.sidebar-collapse-button {
+  border: none;
+  background: var(--color-bg-card);
+  color: var(--color-text-secondary);
+  width: 28px;
+  height: 28px;
+  border-radius: 999px;
+  box-shadow: var(--shadow-sm);
+  cursor: pointer;
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  transition: transform var(--transition-fast), background-color var(--transition-fast);
+}
+
+.sidebar-collapse-button:hover {
+  background: var(--color-bg-hover);
+  transform: scale(1.05);
+}
+
 .sidebar-section {
   margin-bottom: var(--spacing-8);
 }
diff --git a/app/javascript/controllers/sidebar_controller.js b/app/javascript/controllers/sidebar_controller.js
new file mode 100644
index 0000000..a02a3ed
--- /dev/null
+++ b/app/javascript/controllers/sidebar_controller.js
@@ -0,0 +1,161 @@
+import { Controller } from "@hotwired/stimulus"
+
+const STORAGE_WIDTH_KEY = "hackorum-sidebar-width"
+const STORAGE_COLLAPSED_KEY = "hackorum-sidebar-collapsed"
+const DEFAULT_WIDTH = 360
+const MIN_WIDTH = 260
+const MAX_WIDTH = 960
+const MAX_WIDTH_RATIO = 0.75
+
+export default class extends Controller {
+  static targets = ["layout", "sidebar", "resizer", "toggleButton", "toggleIcon"]
+
+  connect() {
+    if (!this.hasLayoutTarget || !this.hasSidebarTarget) {
+      return
+    }
+
+    this.handleWindowResize = this.handleWindowResize.bind(this)
+    window.addEventListener("resize", this.handleWindowResize)
+
+    this.applyStoredState()
+  }
+
+  disconnect() {
+    window.removeEventListener("resize", this.handleWindowResize)
+    this.stopResize()
+  }
+
+  toggle() {
+    if (this.isCollapsed()) {
+      this.expand()
+    } else {
+      this.collapse()
+    }
+  }
+
+  startResize(event) {
+    if (this.isCollapsed()) {
+      return
+    }
+
+    event.preventDefault()
+    this.isResizing = true
+    this.startX = this.clientXFrom(event)
+    this.startWidth = this.sidebarTarget.getBoundingClientRect().width
+
+    this.boundHandleResize = this.handleResize.bind(this)
+    this.boundStopResize = this.stopResize.bind(this)
+
+    document.addEventListener("mousemove", this.boundHandleResize)
+    document.addEventListener("mouseup", this.boundStopResize)
+    document.addEventListener("touchmove", this.boundHandleResize, { passive: false })
+    document.addEventListener("touchend", this.boundStopResize)
+
+    document.body.classList.add("sidebar-resizing")
+  }
+
+  handleResize(event) {
+    if (!this.isResizing) {
+      return
+    }
+
+    event.preventDefault()
+    const delta = this.clientXFrom(event) - this.startX
+    const nextWidth = this.clampWidth(this.startWidth + delta)
+    this.setSidebarWidth(nextWidth)
+  }
+
+  stopResize() {
+    if (!this.isResizing) {
+      return
+    }
+
+    this.isResizing = false
+    document.body.classList.remove("sidebar-resizing")
+
+    document.removeEventListener("mousemove", this.boundHandleResize)
+    document.removeEventListener("mouseup", this.boundStopResize)
+    document.removeEventListener("touchmove", this.boundHandleResize)
+    document.removeEventListener("touchend", this.boundStopResize)
+
+    window.localStorage.setItem(STORAGE_WIDTH_KEY, String(this.currentWidth || this.startWidth || DEFAULT_WIDTH))
+  }
+
+  handleWindowResize() {
+    if (this.isCollapsed()) {
+      return
+    }
+
+    const stored = this.readWidth()
+    this.setSidebarWidth(this.clampWidth(stored))
+  }
+
+  applyStoredState() {
+    const collapsed = window.localStorage.getItem(STORAGE_COLLAPSED_KEY) === "true"
+    if (collapsed) {
+      this.collapse(false)
+      return
+    }
+
+    this.expand(false)
+    this.setSidebarWidth(this.clampWidth(this.readWidth()))
+  }
+
+  collapse(shouldStore = true) {
+    document.body.classList.add("sidebar-collapsed")
+    if (shouldStore) {
+      window.localStorage.setItem(STORAGE_COLLAPSED_KEY, "true")
+    }
+    this.updateToggleIcon()
+  }
+
+  expand(shouldStore = true) {
+    document.body.classList.remove("sidebar-collapsed")
+    if (shouldStore) {
+      window.localStorage.setItem(STORAGE_COLLAPSED_KEY, "false")
+    }
+    this.setSidebarWidth(this.clampWidth(this.readWidth()))
+    this.updateToggleIcon()
+  }
+
+  updateToggleIcon() {
+    if (!this.hasToggleIconTarget) {
+      return
+    }
+
+    this.toggleIconTarget.textContent = this.isCollapsed() ? "▶" : "◀"
+  }
+
+  isCollapsed() {
+    return document.body.classList.contains("sidebar-collapsed")
+  }
+
+  readWidth() {
+    const stored = Number.parseFloat(window.localStorage.getItem(STORAGE_WIDTH_KEY))
+    if (Number.isFinite(stored) && stored > 0) {
+      return stored
+    }
+    return DEFAULT_WIDTH
+  }
+
+  setSidebarWidth(width) {
+    this.currentWidth = width
+    this.layoutTarget.style.setProperty("--sidebar-width", `${width}px`)
+  }
+
+  clampWidth(width) {
+    const maxWidth = Math.max(MIN_WIDTH, Math.min(MAX_WIDTH, Math.round(window.innerWidth * MAX_WIDTH_RATIO)))
+    return Math.min(Math.max(width, MIN_WIDTH), maxWidth)
+  }
+
+  clientXFrom(event) {
+    if (event.touches && event.touches.length > 0) {
+      return event.touches[0].clientX
+    }
+    if (event.changedTouches && event.changedTouches.length > 0) {
+      return event.changedTouches[0].clientX
+    }
+    return event.clientX
+  }
+}
diff --git a/app/views/layouts/application.html.slim b/app/views/layouts/application.html.slim
index c0d321d..ad43ac8 100644
--- a/app/views/layouts/application.html.slim
+++ b/app/views/layouts/application.html.slim
@@ -65,9 +65,12 @@ html data-theme="light"
               = link_to "Register", new_registration_path, class: "nav-link"
 
     - if content_for?(:sidebar)
-      .page-layout.with-sidebar
-        .layout-sidebar
+      .page-layout.with-sidebar data-controller="sidebar" data-sidebar-target="layout"
+        .layout-sidebar#layout-sidebar data-sidebar-target="sidebar"
           = yield :sidebar
+        .layout-sidebar-resizer data-sidebar-target="resizer" role="separator" aria-orientation="vertical" aria-label="Resize sidebar" data-action="mousedown->sidebar#startResize touchstart->sidebar#startResize"
+          button.sidebar-collapse-button type="button" aria-label="Toggle sidebar" data-action="click->sidebar#toggle" data-sidebar-target="toggleButton"
+            span data-sidebar-target="toggleIcon" ◀
         main.container
           - flash.each do |type, message|
             .flash class=type