diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7b67389a430c..42f65a4894b7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -64,6 +64,7 @@
 
 ### Chore & Maintenance
 
+- `[jest-circus]` Standardize file naming in `jest-circus` ([#7301](https://github.com/facebook/jest/pull/7301))
 - `[docs]` Add synchronous test.each setup ([#7150](https://github.com/facebook/jest/pull/7150))
 - `[docs]` Add `this.extend` to the Custom Matchers API reference ([#7130](https://github.com/facebook/jest/pull/7130))
 - `[docs]` Fix default value for `coverageReporters` value in configuration docs ([#7126](https://github.com/facebook/jest/pull/7126))
diff --git a/packages/jest-circus/runner.js b/packages/jest-circus/runner.js
index 214956a9f42a..8ed8163ee414 100644
--- a/packages/jest-circus/runner.js
+++ b/packages/jest-circus/runner.js
@@ -9,5 +9,5 @@
  */
 
 // Allow people to use `jest-circus/runner` as a runner.
-const runner = require('./build/legacy_code_todo_rewrite/jest_adapter');
+const runner = require('./build/legacy-code-todo-rewrite/jestAdapter');
 module.exports = runner;
diff --git a/packages/jest-circus/src/__mocks__/test_event_handler.js b/packages/jest-circus/src/__mocks__/testEventHandler.js
similarity index 100%
rename from packages/jest-circus/src/__mocks__/test_event_handler.js
rename to packages/jest-circus/src/__mocks__/testEventHandler.js
diff --git a/packages/jest-circus/src/__mocks__/test_utils.js b/packages/jest-circus/src/__mocks__/testUtils.js
similarity index 97%
rename from packages/jest-circus/src/__mocks__/test_utils.js
rename to packages/jest-circus/src/__mocks__/testUtils.js
index 39594b009a2b..4e3ca543dccb 100644
--- a/packages/jest-circus/src/__mocks__/test_utils.js
+++ b/packages/jest-circus/src/__mocks__/testUtils.js
@@ -20,7 +20,7 @@ import {skipSuiteOnWindows} from '../../../../scripts/ConditionalTest';
 const CIRCUS_PATH = require.resolve('../../build/index');
 const CIRCUS_RUN_PATH = require.resolve('../../build/run');
 const CIRCUS_STATE_PATH = require.resolve('../../build/state');
-const TEST_EVENT_HANDLER_PATH = require.resolve('./test_event_handler');
+const TEST_EVENT_HANDLER_PATH = require.resolve('./testEventHandler');
 const BABEL_REGISTER_PATH = require.resolve('babel-register');
 
 skipSuiteOnWindows();
diff --git a/packages/jest-circus/src/__tests__/__snapshots__/after_all.test.js.snap b/packages/jest-circus/src/__tests__/__snapshots__/afterAll.test.js.snap
similarity index 100%
rename from packages/jest-circus/src/__tests__/__snapshots__/after_all.test.js.snap
rename to packages/jest-circus/src/__tests__/__snapshots__/afterAll.test.js.snap
diff --git a/packages/jest-circus/src/__tests__/__snapshots__/base_test.test.js.snap b/packages/jest-circus/src/__tests__/__snapshots__/baseTest.test.js.snap
similarity index 100%
rename from packages/jest-circus/src/__tests__/__snapshots__/base_test.test.js.snap
rename to packages/jest-circus/src/__tests__/__snapshots__/baseTest.test.js.snap
diff --git a/packages/jest-circus/src/__tests__/after_all.test.js b/packages/jest-circus/src/__tests__/afterAll.test.js
similarity index 97%
rename from packages/jest-circus/src/__tests__/after_all.test.js
rename to packages/jest-circus/src/__tests__/afterAll.test.js
index 22e424d96f20..7cccc1f66d49 100644
--- a/packages/jest-circus/src/__tests__/after_all.test.js
+++ b/packages/jest-circus/src/__tests__/afterAll.test.js
@@ -10,7 +10,7 @@
 
 'use strict';
 
-import {runTest} from '../__mocks__/test_utils';
+import {runTest} from '../__mocks__/testUtils';
 
 test('tests are not marked done until their parent afterAll runs', () => {
   const {stdout} = runTest(`
diff --git a/packages/jest-circus/src/__tests__/base_test.test.js b/packages/jest-circus/src/__tests__/baseTest.test.js
similarity index 94%
rename from packages/jest-circus/src/__tests__/base_test.test.js
rename to packages/jest-circus/src/__tests__/baseTest.test.js
index ec83663ba8db..1cc1c2abab94 100644
--- a/packages/jest-circus/src/__tests__/base_test.test.js
+++ b/packages/jest-circus/src/__tests__/baseTest.test.js
@@ -10,7 +10,7 @@
 
 'use strict';
 
-import {runTest} from '../__mocks__/test_utils';
+import {runTest} from '../__mocks__/testUtils';
 
 test('simple test', () => {
   const {stdout} = runTest(`
diff --git a/packages/jest-circus/src/__tests__/circus_it_test_error.test.js b/packages/jest-circus/src/__tests__/circusItTestError.test.js
similarity index 100%
rename from packages/jest-circus/src/__tests__/circus_it_test_error.test.js
rename to packages/jest-circus/src/__tests__/circusItTestError.test.js
diff --git a/packages/jest-circus/src/__tests__/circus_todo_test_error.test.js b/packages/jest-circus/src/__tests__/circusItTodoTestError.test.js
similarity index 100%
rename from packages/jest-circus/src/__tests__/circus_todo_test_error.test.js
rename to packages/jest-circus/src/__tests__/circusItTodoTestError.test.js
diff --git a/packages/jest-circus/src/__tests__/hooks.test.js b/packages/jest-circus/src/__tests__/hooks.test.js
index 2486cc3d6e62..6d9b58bce341 100644
--- a/packages/jest-circus/src/__tests__/hooks.test.js
+++ b/packages/jest-circus/src/__tests__/hooks.test.js
@@ -10,7 +10,7 @@
 
 'use strict';
 
-import {runTest} from '../__mocks__/test_utils';
+import {runTest} from '../__mocks__/testUtils';
 
 test('beforeEach is executed before each test in current/child describe blocks', () => {
   const {stdout} = runTest(`
diff --git a/packages/jest-circus/src/__tests__/hooks_error.test.js b/packages/jest-circus/src/__tests__/hooksError.test.js
similarity index 100%
rename from packages/jest-circus/src/__tests__/hooks_error.test.js
rename to packages/jest-circus/src/__tests__/hooksError.test.js
diff --git a/packages/jest-circus/src/event_handler.js b/packages/jest-circus/src/eventHandler.js
similarity index 97%
rename from packages/jest-circus/src/event_handler.js
rename to packages/jest-circus/src/eventHandler.js
index fb5af141b802..893e61f61410 100644
--- a/packages/jest-circus/src/event_handler.js
+++ b/packages/jest-circus/src/eventHandler.js
@@ -20,12 +20,12 @@ import {
 import {
   injectGlobalErrorHandlers,
   restoreGlobalErrorHandlers,
-} from './error_handlers';
+} from './globalErrorHandlers';
 
 // To pass this value from Runtime object to state we need to use global[sym]
 const TEST_TIMEOUT_SYMBOL = Symbol.for('TEST_TIMEOUT_SYMBOL');
 
-const handler: EventHandler = (event, state): void => {
+const eventHandler: EventHandler = (event, state): void => {
   switch (event.name) {
     case 'include_test_location_in_result': {
       state.includeTestLocationInResult = true;
@@ -183,4 +183,4 @@ const handler: EventHandler = (event, state): void => {
   }
 };
 
-export default handler;
+export default eventHandler;
diff --git a/packages/jest-circus/src/format_node_assert_errors.js b/packages/jest-circus/src/formatNodeAssertErrors.js
similarity index 97%
rename from packages/jest-circus/src/format_node_assert_errors.js
rename to packages/jest-circus/src/formatNodeAssertErrors.js
index 9151fa9fe3fa..d6080ce0b168 100644
--- a/packages/jest-circus/src/format_node_assert_errors.js
+++ b/packages/jest-circus/src/formatNodeAssertErrors.js
@@ -43,7 +43,7 @@ const humanReadableOperators = {
   strictEqual: 'to strictly be equal',
 };
 
-export default (event: Event, state: State) => {
+const formatNodeAssertErrors = (event: Event, state: State) => {
   switch (event.name) {
     case 'test_done': {
       event.test.errors = event.test.errors.map(errors => {
@@ -167,3 +167,5 @@ function assertionErrorMessage(error: AssertionError, options: DiffOptions) {
     trimmedStack
   );
 }
+
+export default formatNodeAssertErrors;
diff --git a/packages/jest-circus/src/error_handlers.js b/packages/jest-circus/src/globalErrorHandlers.js
similarity index 100%
rename from packages/jest-circus/src/error_handlers.js
rename to packages/jest-circus/src/globalErrorHandlers.js
diff --git a/packages/jest-circus/src/legacy_code_todo_rewrite/jest_adapter.js b/packages/jest-circus/src/legacy-code-todo-rewrite/jestAdapter.js
similarity index 95%
rename from packages/jest-circus/src/legacy_code_todo_rewrite/jest_adapter.js
rename to packages/jest-circus/src/legacy-code-todo-rewrite/jestAdapter.js
index bf2d87b9f4bd..af85e4d095b4 100644
--- a/packages/jest-circus/src/legacy_code_todo_rewrite/jest_adapter.js
+++ b/packages/jest-circus/src/legacy-code-todo-rewrite/jestAdapter.js
@@ -12,7 +12,7 @@ import type {GlobalConfig, ProjectConfig} from 'types/Config';
 import type {TestResult} from 'types/TestResult';
 import type Runtime from 'jest-runtime';
 
-const FRAMEWORK_INITIALIZER = require.resolve('./jest_adapter_init');
+const FRAMEWORK_INITIALIZER = require.resolve('./jestAdapterInit');
 import path from 'path';
 
 const jestAdapter = async (
@@ -28,7 +28,7 @@ const jestAdapter = async (
   } = runtime.requireInternalModule(FRAMEWORK_INITIALIZER);
 
   runtime
-    .requireInternalModule(path.resolve(__dirname, './jest_expect.js'))
+    .requireInternalModule(path.resolve(__dirname, './jestExpect.js'))
     .default({
       expand: globalConfig.expand,
     });
diff --git a/packages/jest-circus/src/legacy_code_todo_rewrite/jest_adapter_init.js b/packages/jest-circus/src/legacy-code-todo-rewrite/jestAdapterInit.js
similarity index 100%
rename from packages/jest-circus/src/legacy_code_todo_rewrite/jest_adapter_init.js
rename to packages/jest-circus/src/legacy-code-todo-rewrite/jestAdapterInit.js
diff --git a/packages/jest-circus/src/legacy_code_todo_rewrite/jest_expect.js b/packages/jest-circus/src/legacy-code-todo-rewrite/jestExpect.js
similarity index 100%
rename from packages/jest-circus/src/legacy_code_todo_rewrite/jest_expect.js
rename to packages/jest-circus/src/legacy-code-todo-rewrite/jestExpect.js
diff --git a/packages/jest-circus/src/state.js b/packages/jest-circus/src/state.js
index 3187775bcc2f..36d4fa69cf04 100644
--- a/packages/jest-circus/src/state.js
+++ b/packages/jest-circus/src/state.js
@@ -10,8 +10,8 @@
 import type {Event, State, EventHandler} from 'types/Circus';
 
 import {makeDescribe} from './utils';
-import eventHandler from './event_handler';
-import formatNodeAssertErrors from './format_node_assert_errors';
+import eventHandler from './eventHandler';
+import formatNodeAssertErrors from './formatNodeAssertErrors';
 
 const eventHandlers: Array<EventHandler> = [
   eventHandler,