diff --git a/.changeset/beige-baboons-promise.md b/.changeset/beige-baboons-promise.md
new file mode 100644
index 0000000000..e313a85f1a
--- /dev/null
+++ b/.changeset/beige-baboons-promise.md
@@ -0,0 +1,5 @@
+---
+'@lit-labs/observers': major
+---
+
+Change filenames to match project convention: replace `_` with `-`.
diff --git a/.eslintignore b/.eslintignore
index 65091ffbf2..82edcd40a5 100644
--- a/.eslintignore
+++ b/.eslintignore
@@ -239,10 +239,11 @@ packages/labs/observers/development/
 packages/labs/observers/test/
 packages/labs/observers/node_modules/
 packages/labs/observers/index.*
-packages/labs/observers/mutation_controller.*
-packages/labs/observers/performance_controller.*
-packages/labs/observers/resize_controller.*
-packages/labs/observers/intersection_controller.*
+packages/labs/observers/mutation-controller.*
+packages/labs/observers/performance-controller.*
+packages/labs/observers/resize-controller.*
+packages/labs/observers/intersection-controller.*
+
 packages/labs/react/development/
 packages/labs/react/test/
 packages/labs/react/node_modules/
diff --git a/.prettierignore b/.prettierignore
index 3ad2cb103c..23da6b0e2d 100644
--- a/.prettierignore
+++ b/.prettierignore
@@ -226,10 +226,11 @@ packages/labs/observers/development/
 packages/labs/observers/test/
 packages/labs/observers/node_modules/
 packages/labs/observers/index.*
-packages/labs/observers/mutation_controller.*
-packages/labs/observers/performance_controller.*
-packages/labs/observers/resize_controller.*
-packages/labs/observers/intersection_controller.*
+packages/labs/observers/mutation-controller.*
+packages/labs/observers/performance-controller.*
+packages/labs/observers/resize-controller.*
+packages/labs/observers/intersection-controller.*
+
 packages/labs/react/development/
 packages/labs/react/test/
 packages/labs/react/node_modules/
diff --git a/packages/labs/observers/.gitignore b/packages/labs/observers/.gitignore
index 479acfe54a..cfefc0bfd4 100644
--- a/packages/labs/observers/.gitignore
+++ b/packages/labs/observers/.gitignore
@@ -2,7 +2,7 @@
 /test/
 /node_modules/
 /index.*
-/mutation_controller.*
-/performance_controller.*
-/resize_controller.*
-/intersection_controller.*
\ No newline at end of file
+/mutation-controller.*
+/performance-controller.*
+/resize-controller.*
+/intersection-controller.*
diff --git a/packages/labs/observers/package.json b/packages/labs/observers/package.json
index 63d1a1794b..2b8a5921ba 100644
--- a/packages/labs/observers/package.json
+++ b/packages/labs/observers/package.json
@@ -22,35 +22,35 @@
       "development": "./development/index.js",
       "default": "./index.js"
     },
-    "./mutation_controller.js": {
-      "types": "./development/mutation_controller.d.ts",
-      "development": "./development/mutation_controller.js",
-      "default": "./mutation_controller.js"
+    "./mutation-controller.js": {
+      "types": "./development/mutation-controller.d.ts",
+      "development": "./development/mutation-controller.js",
+      "default": "./mutation-controller.js"
     },
-    "./performance_controller.js": {
-      "types": "./development/performance_controller.d.ts",
-      "development": "./development/performance_controller.js",
-      "default": "./performance_controller.js"
+    "./performance-controller.js": {
+      "types": "./development/performance-controller.d.ts",
+      "development": "./development/performance-controller.js",
+      "default": "./performance-controller.js"
     },
-    "./resize_controller.js": {
-      "types": "./development/resize_controller.d.ts",
-      "development": "./development/resize_controller.js",
-      "default": "./resize_controller.js"
+    "./resize-controller.js": {
+      "types": "./development/resize-controller.d.ts",
+      "development": "./development/resize-controller.js",
+      "default": "./resize-controller.js"
     },
-    "./intersection_controller.js": {
-      "types": "./development/intersection_controller.d.ts",
-      "development": "./development/intersection_controller.js",
-      "default": "./intersection_controller.js"
+    "./intersection-controller.js": {
+      "types": "./development/intersection-controller.d.ts",
+      "development": "./development/intersection-controller.js",
+      "default": "./intersection-controller.js"
     }
   },
   "files": [
     "/development/",
     "!/development/test/",
     "/index.{d.ts,d.ts.map,js,js.map}",
-    "/mutation_controller.{d.ts,d.ts.map,js,js.map}",
-    "/performance_controller.{d.ts,d.ts.map,js,js.map}",
-    "/resize_controller.{d.ts,d.ts.map,js,js.map}",
-    "/intersection_controller.{d.ts,d.ts.map,js,js.map}"
+    "/mutation-controller.{d.ts,d.ts.map,js,js.map}",
+    "/performance-controller.{d.ts,d.ts.map,js,js.map}",
+    "/resize-controller.{d.ts,d.ts.map,js,js.map}",
+    "/intersection-controller.{d.ts,d.ts.map,js,js.map}"
   ],
   "scripts": {
     "build": "wireit",
@@ -109,10 +109,10 @@
       ],
       "output": [
         "index.js{,.map}",
-        "intersection_controller.js{,.map}",
-        "mutation_controller.js{,.map}",
-        "performance_controller.js{,.map}",
-        "resize_controller.js{,.map}",
+        "intersection-controller.js{,.map}",
+        "mutation-controller.js{,.map}",
+        "performance-controller.js{,.map}",
+        "resize-controller.js{,.map}",
         "test/**/*.js{,.map}"
       ]
     },
diff --git a/packages/labs/observers/rollup.config.js b/packages/labs/observers/rollup.config.js
index 3b4cbb8f0b..0b270d5eb5 100644
--- a/packages/labs/observers/rollup.config.js
+++ b/packages/labs/observers/rollup.config.js
@@ -11,10 +11,10 @@ export default litProdConfig({
   packageName: createRequire(import.meta.url)('./package.json').name,
   entryPoints: [
     'index',
-    'mutation_controller',
-    'resize_controller',
-    'intersection_controller',
-    'performance_controller',
+    'mutation-controller',
+    'resize-controller',
+    'intersection-controller',
+    'performance-controller',
   ],
   external: ['@lit/reactive-element'],
 });
diff --git a/packages/labs/observers/src/intersection_controller.ts b/packages/labs/observers/src/intersection-controller.ts
similarity index 100%
rename from packages/labs/observers/src/intersection_controller.ts
rename to packages/labs/observers/src/intersection-controller.ts
diff --git a/packages/labs/observers/src/mutation_controller.ts b/packages/labs/observers/src/mutation-controller.ts
similarity index 100%
rename from packages/labs/observers/src/mutation_controller.ts
rename to packages/labs/observers/src/mutation-controller.ts
diff --git a/packages/labs/observers/src/performance_controller.ts b/packages/labs/observers/src/performance-controller.ts
similarity index 100%
rename from packages/labs/observers/src/performance_controller.ts
rename to packages/labs/observers/src/performance-controller.ts
diff --git a/packages/labs/observers/src/resize_controller.ts b/packages/labs/observers/src/resize-controller.ts
similarity index 100%
rename from packages/labs/observers/src/resize_controller.ts
rename to packages/labs/observers/src/resize-controller.ts
diff --git a/packages/labs/observers/src/test/intersection_controller_test.ts b/packages/labs/observers/src/test/intersection-controller_test.ts
similarity index 99%
rename from packages/labs/observers/src/test/intersection_controller_test.ts
rename to packages/labs/observers/src/test/intersection-controller_test.ts
index d8867e22d0..d20ef0a8cc 100644
--- a/packages/labs/observers/src/test/intersection_controller_test.ts
+++ b/packages/labs/observers/src/test/intersection-controller_test.ts
@@ -13,7 +13,7 @@ import {
   IntersectionController,
   IntersectionControllerConfig,
   IntersectionValueCallback,
-} from '@lit-labs/observers/intersection_controller.js';
+} from '@lit-labs/observers/intersection-controller.js';
 import {generateElementName, nextFrame} from './test-helpers.js';
 import {assert} from '@esm-bundle/chai';
 
diff --git a/packages/labs/observers/src/test/mutation_controller_test.ts b/packages/labs/observers/src/test/mutation-controller_test.ts
similarity index 99%
rename from packages/labs/observers/src/test/mutation_controller_test.ts
rename to packages/labs/observers/src/test/mutation-controller_test.ts
index da38ff9e24..f4b4bd626e 100644
--- a/packages/labs/observers/src/test/mutation_controller_test.ts
+++ b/packages/labs/observers/src/test/mutation-controller_test.ts
@@ -13,7 +13,7 @@ import {
   MutationController,
   MutationControllerConfig,
   MutationValueCallback,
-} from '@lit-labs/observers/mutation_controller.js';
+} from '@lit-labs/observers/mutation-controller.js';
 import {generateElementName, nextFrame} from './test-helpers.js';
 import {assert} from '@esm-bundle/chai';
 
diff --git a/packages/labs/observers/src/test/performance_controller_test.ts b/packages/labs/observers/src/test/performance-controller_test.ts
similarity index 99%
rename from packages/labs/observers/src/test/performance_controller_test.ts
rename to packages/labs/observers/src/test/performance-controller_test.ts
index 028c56eb51..7342f58218 100644
--- a/packages/labs/observers/src/test/performance_controller_test.ts
+++ b/packages/labs/observers/src/test/performance-controller_test.ts
@@ -13,7 +13,7 @@ import {
   PerformanceController,
   PerformanceControllerConfig,
   PerformanceValueCallback,
-} from '@lit-labs/observers/performance_controller.js';
+} from '@lit-labs/observers/performance-controller.js';
 import {generateElementName, nextFrame} from './test-helpers.js';
 import {assert} from '@esm-bundle/chai';
 
diff --git a/packages/labs/observers/src/test/resize_controller_test.ts b/packages/labs/observers/src/test/resize-controller_test.ts
similarity index 99%
rename from packages/labs/observers/src/test/resize_controller_test.ts
rename to packages/labs/observers/src/test/resize-controller_test.ts
index 13b3efb138..7a6de19900 100644
--- a/packages/labs/observers/src/test/resize_controller_test.ts
+++ b/packages/labs/observers/src/test/resize-controller_test.ts
@@ -13,7 +13,7 @@ import {
   ResizeController,
   ResizeControllerConfig,
   ResizeValueCallback,
-} from '@lit-labs/observers/resize_controller.js';
+} from '@lit-labs/observers/resize-controller.js';
 import {generateElementName, nextFrame} from './test-helpers.js';
 import {assert} from '@esm-bundle/chai';
 
@@ -474,7 +474,7 @@ if (DEV_MODE) {
     // This test only checks compile-type behavior. There are no runtime checks.
     const el = await getTestElement();
     const A = new ResizeController<number>(el, {
-      // @ts-expect-error Type 'string' is not assignable to type 'number'
+      // @ts-expect-error Type 'number' is not assignable to type 'string'
       callback: () => '',
     });
     if (A) {
@@ -484,11 +484,11 @@ if (DEV_MODE) {
     const B = new ResizeController(el, {
       callback: () => '',
     });
-    // @ts-expect-error Type 'number' is not assignable to type 'string'.
+    // @ts-expect-error Type 'number' is not assignable to type 'string'
     B.value = 2;
 
     const C = new ResizeController(el, {}) as ResizeController<string>;
-    // @ts-expect-error Type 'number' is not assignable to type 'string'.
+    // @ts-expect-error Type 'number' is not assignable to type 'string'
     C.value = 3;
 
     const narrowTypeCb: ResizeValueCallback<string | null> = () => '';