diff --git a/doc/api/test.md b/doc/api/test.md
index 29d071e668b8c6..be5c63c6e8e613 100644
--- a/doc/api/test.md
+++ b/doc/api/test.md
@@ -3720,6 +3720,39 @@ added: v25.0.0
 
 Number of times the test has been attempted.
 
+### `context.workerId`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* Type: {number|undefined}
+
+The unique identifier of the worker running the current test file. This value is
+derived from the `NODE_TEST_WORKER_ID` environment variable. When running tests
+with `--test-isolation=process` (the default), each test file runs in a separate
+child process and is assigned a worker ID from 1 to N, where N is the number of
+concurrent workers. When running with `--test-isolation=none`, all tests run in
+the same process and the worker ID is always 1. This value is `undefined` when
+not running in a test context.
+
+This property is useful for splitting resources (like database connections or
+server ports) across concurrent test files:
+
+```mjs
+import { test } from 'node:test';
+import { process } from 'node:process';
+
+test('database operations', async (t) => {
+  // Worker ID is available via context
+  console.log(`Running in worker ${t.workerId}`);
+
+  // Or via environment variable (available at import time)
+  const workerId = process.env.NODE_TEST_WORKER_ID;
+  // Use workerId to allocate separate resources per worker
+});
+```
+
 ### `context.plan(count[,options])`
 
 <!-- YAML
diff --git a/lib/internal/test_runner/runner.js b/lib/internal/test_runner/runner.js
index 3f9e855f755212..e5de8563dbc7ef 100644
--- a/lib/internal/test_runner/runner.js
+++ b/lib/internal/test_runner/runner.js
@@ -15,6 +15,7 @@ const {
   ArrayPrototypeSlice,
   ArrayPrototypeSome,
   ArrayPrototypeSort,
+  MathMax,
   ObjectAssign,
   PromisePrototypeThen,
   PromiseWithResolvers,
@@ -23,6 +24,7 @@ const {
   SafePromiseAllReturnVoid,
   SafePromiseAllSettledReturnVoid,
   SafeSet,
+  String,
   StringPrototypeIndexOf,
   StringPrototypeSlice,
   StringPrototypeStartsWith,
@@ -33,6 +35,7 @@ const {
 
 const { spawn } = require('child_process');
 const { finished } = require('internal/streams/end-of-stream');
+const { availableParallelism } = require('os');
 const { resolve, sep, isAbsolute } = require('path');
 const { DefaultDeserializer, DefaultSerializer } = require('v8');
 const { getOptionValue, getOptionsAsFlagsFromBinding } = require('internal/options');
@@ -117,6 +120,21 @@ const kCanceledTests = new SafeSet()
 
 let kResistStopPropagation;
 
+// Worker ID pool management for concurrent test execution
+class WorkerIdPool {
+  #nextId = 0;
+  #maxConcurrency;
+
+  constructor(maxConcurrency) {
+    this.#maxConcurrency = maxConcurrency;
+  }
+
+  acquire() {
+    const id = (this.#nextId++ % this.#maxConcurrency) + 1;
+    return id;
+  }
+}
+
 function createTestFileList(patterns, cwd) {
   const hasUserSuppliedPattern = patterns != null;
   if (!patterns || patterns.length === 0) {
@@ -404,6 +422,15 @@ function runTestFile(path, filesWatcher, opts) {
     const args = getRunArgs(path, opts);
     const stdio = ['pipe', 'pipe', 'pipe'];
     const env = { __proto__: null, ...process.env, NODE_TEST_CONTEXT: 'child-v8' };
+
+    // Acquire a worker ID from the pool for process isolation mode
+    let workerId;
+    if (opts.workerIdPool) {
+      workerId = opts.workerIdPool.acquire();
+      env.NODE_TEST_WORKER_ID = String(workerId);
+      debug('Assigned worker ID %d to test file: %s', workerId, path);
+    }
+
     if (watchMode) {
       stdio.push('ipc');
       env.WATCH_REPORT_DEPENDENCIES = '1';
@@ -747,6 +774,25 @@ function run(options = kEmptyObject) {
   let postRun;
   let filesWatcher;
   let runFiles;
+
+  // Create worker ID pool for concurrent test execution.
+  // Use concurrency from globalOptions which has been processed by parseCommandLine().
+  const effectiveConcurrency = globalOptions.concurrency ?? concurrency;
+  let maxConcurrency = 1;
+  if (effectiveConcurrency === true) {
+    maxConcurrency = MathMax(availableParallelism() - 1, 1);
+  } else if (typeof effectiveConcurrency === 'number') {
+    maxConcurrency = effectiveConcurrency;
+  }
+  const workerIdPool = new WorkerIdPool(maxConcurrency);
+  debug(
+    'Created worker ID pool with max concurrency: %d, ' +
+    'effectiveConcurrency: %s, testFiles: %d',
+    maxConcurrency,
+    effectiveConcurrency,
+    testFiles.length,
+  );
+
   const opts = {
     __proto__: null,
     root,
@@ -763,6 +809,7 @@ function run(options = kEmptyObject) {
     argv,
     execArgv,
     rerunFailuresFilePath,
+    workerIdPool: isolation === 'process' ? workerIdPool : null,
   };
 
   if (isolation === 'process') {
@@ -789,6 +836,10 @@ function run(options = kEmptyObject) {
       });
     };
   } else if (isolation === 'none') {
+    // For isolation=none, set worker ID to 1 in the current process
+    process.env.NODE_TEST_WORKER_ID = '1';
+    debug('Set NODE_TEST_WORKER_ID=1 for isolation=none');
+
     if (watch) {
       const absoluteTestFiles = ArrayPrototypeMap(testFiles, (file) => (isAbsolute(file) ? file : resolve(cwd, file)));
       filesWatcher = watchFiles(absoluteTestFiles, opts);
diff --git a/lib/internal/test_runner/test.js b/lib/internal/test_runner/test.js
index 0f2265bb74366a..5e92d40c995600 100644
--- a/lib/internal/test_runner/test.js
+++ b/lib/internal/test_runner/test.js
@@ -284,6 +284,11 @@ class TestContext {
     return this.#test.attempt ?? 0;
   }
 
+  get workerId() {
+    const envWorkerId = process.env.NODE_TEST_WORKER_ID;
+    return Number(envWorkerId) || undefined;
+  }
+
   diagnostic(message) {
     this.#test.diagnostic(message);
   }
diff --git a/test/fixtures/test-runner/worker-id/test-1.mjs b/test/fixtures/test-runner/worker-id/test-1.mjs
new file mode 100644
index 00000000000000..7e6f40f2b18c38
--- /dev/null
+++ b/test/fixtures/test-runner/worker-id/test-1.mjs
@@ -0,0 +1,26 @@
+import { test } from 'node:test';
+
+test('worker ID is available as environment variable', (t) => {
+	const workerId = process.env.NODE_TEST_WORKER_ID;
+	if (workerId === undefined) {
+		throw new Error('NODE_TEST_WORKER_ID should be defined');
+	}
+
+	const id = Number(workerId);
+	if (isNaN(id) || id < 1) {
+		throw new Error(`Invalid worker ID: ${workerId}`);
+	}
+});
+
+test('worker ID is available via context', (t) => {
+	const workerId = t.workerId;
+	const envWorkerId = process.env.NODE_TEST_WORKER_ID;
+
+	if (workerId === undefined) {
+		throw new Error('context.workerId should be defined');
+	}
+
+	if (workerId !== Number(envWorkerId)) {
+		throw new Error(`context.workerId (${workerId}) should match NODE_TEST_WORKER_ID (${envWorkerId})`);
+	}
+});
diff --git a/test/fixtures/test-runner/worker-id/test-2.mjs b/test/fixtures/test-runner/worker-id/test-2.mjs
new file mode 100644
index 00000000000000..7e6f40f2b18c38
--- /dev/null
+++ b/test/fixtures/test-runner/worker-id/test-2.mjs
@@ -0,0 +1,26 @@
+import { test } from 'node:test';
+
+test('worker ID is available as environment variable', (t) => {
+	const workerId = process.env.NODE_TEST_WORKER_ID;
+	if (workerId === undefined) {
+		throw new Error('NODE_TEST_WORKER_ID should be defined');
+	}
+
+	const id = Number(workerId);
+	if (isNaN(id) || id < 1) {
+		throw new Error(`Invalid worker ID: ${workerId}`);
+	}
+});
+
+test('worker ID is available via context', (t) => {
+	const workerId = t.workerId;
+	const envWorkerId = process.env.NODE_TEST_WORKER_ID;
+
+	if (workerId === undefined) {
+		throw new Error('context.workerId should be defined');
+	}
+
+	if (workerId !== Number(envWorkerId)) {
+		throw new Error(`context.workerId (${workerId}) should match NODE_TEST_WORKER_ID (${envWorkerId})`);
+	}
+});
diff --git a/test/fixtures/test-runner/worker-id/test-3.mjs b/test/fixtures/test-runner/worker-id/test-3.mjs
new file mode 100644
index 00000000000000..7e6f40f2b18c38
--- /dev/null
+++ b/test/fixtures/test-runner/worker-id/test-3.mjs
@@ -0,0 +1,26 @@
+import { test } from 'node:test';
+
+test('worker ID is available as environment variable', (t) => {
+	const workerId = process.env.NODE_TEST_WORKER_ID;
+	if (workerId === undefined) {
+		throw new Error('NODE_TEST_WORKER_ID should be defined');
+	}
+
+	const id = Number(workerId);
+	if (isNaN(id) || id < 1) {
+		throw new Error(`Invalid worker ID: ${workerId}`);
+	}
+});
+
+test('worker ID is available via context', (t) => {
+	const workerId = t.workerId;
+	const envWorkerId = process.env.NODE_TEST_WORKER_ID;
+
+	if (workerId === undefined) {
+		throw new Error('context.workerId should be defined');
+	}
+
+	if (workerId !== Number(envWorkerId)) {
+		throw new Error(`context.workerId (${workerId}) should match NODE_TEST_WORKER_ID (${envWorkerId})`);
+	}
+});
diff --git a/test/parallel/test-runner-worker-id.js b/test/parallel/test-runner-worker-id.js
new file mode 100644
index 00000000000000..9366cfb4fd8a64
--- /dev/null
+++ b/test/parallel/test-runner-worker-id.js
@@ -0,0 +1,141 @@
+'use strict';
+require('../common');
+const fixtures = require('../common/fixtures');
+const assert = require('node:assert');
+const { spawnSync } = require('node:child_process');
+const { test } = require('node:test');
+
+test('NODE_TEST_WORKER_ID is set for concurrent test files', async () => {
+  const args = [
+    '--test',
+    fixtures.path('test-runner', 'worker-id', 'test-1.mjs'),
+    fixtures.path('test-runner', 'worker-id', 'test-2.mjs'),
+    fixtures.path('test-runner', 'worker-id', 'test-3.mjs'),
+  ];
+  const result = spawnSync(process.execPath, args, {
+    cwd: fixtures.path(),
+    env: { ...process.env }
+  });
+
+  assert.strictEqual(result.status, 0, `Test failed: ${result.stderr.toString()}`);
+});
+
+test('NODE_TEST_WORKER_ID is set with explicit concurrency', async () => {
+  const args = [
+    '--test',
+    '--test-concurrency=2',
+    fixtures.path('test-runner', 'worker-id', 'test-1.mjs'),
+    fixtures.path('test-runner', 'worker-id', 'test-2.mjs'),
+  ];
+  const result = spawnSync(process.execPath, args, {
+    cwd: fixtures.path(),
+    env: { ...process.env }
+  });
+
+  assert.strictEqual(result.status, 0, `Test failed: ${result.stderr.toString()}`);
+});
+
+test('NODE_TEST_WORKER_ID is 1 with concurrency=1', async () => {
+  const args = ['--test', '--test-concurrency=1', fixtures.path('test-runner', 'worker-id', 'test-1.mjs')];
+  const result = spawnSync(process.execPath, args, {
+    cwd: fixtures.path(),
+    env: { ...process.env }
+  });
+
+  assert.strictEqual(result.status, 0, `Test failed: ${result.stderr.toString()}`);
+});
+
+test('NODE_TEST_WORKER_ID with explicit isolation=process', async () => {
+  const args = [
+    '--test',
+    '--test-isolation=process',
+    fixtures.path('test-runner', 'worker-id', 'test-1.mjs'),
+    fixtures.path('test-runner', 'worker-id', 'test-2.mjs'),
+  ];
+  const result = spawnSync(process.execPath, args, {
+    cwd: fixtures.path(),
+    env: { ...process.env }
+  });
+
+  assert.strictEqual(result.status, 0, `Test failed: ${result.stderr.toString()}`);
+});
+
+test('NODE_TEST_WORKER_ID is 1 with isolation=none', async () => {
+  const args = [
+    '--test',
+    '--test-isolation=none',
+    fixtures.path('test-runner', 'worker-id', 'test-1.mjs'),
+    fixtures.path('test-runner', 'worker-id', 'test-2.mjs'),
+  ];
+  const result = spawnSync(process.execPath, args, {
+    cwd: fixtures.path(),
+    env: { ...process.env }
+  });
+
+  assert.strictEqual(result.status, 0, `Test failed: ${result.stderr.toString()}`);
+});
+
+test('context.workerId matches NODE_TEST_WORKER_ID', async () => {
+  const args = ['--test', fixtures.path('test-runner', 'worker-id', 'test-1.mjs')];
+  const result = spawnSync(process.execPath, args, {
+    cwd: fixtures.path(),
+    env: { ...process.env }
+  });
+
+  // The fixture tests already verify that context.workerId matches the env var
+  assert.strictEqual(result.status, 0, `Test failed: ${result.stderr.toString()}`);
+});
+
+test('worker IDs are reused when more tests than concurrency', async () => {
+  const tmpdir = require('../common/tmpdir');
+  const { writeFileSync } = require('node:fs');
+  tmpdir.refresh();
+
+  // Create 9 separate test files dynamically
+  const testFiles = [];
+  const usageFile = tmpdir.resolve('worker-usage.txt');
+  for (let i = 1; i <= 9; i++) {
+    const testFile = tmpdir.resolve(`reuse-test-${i}.mjs`);
+    writeFileSync(
+      testFile,
+      `import { test } from 'node:test';
+import { appendFileSync } from 'node:fs';
+
+test('track worker ${i}', () => {
+  const workerId = process.env.NODE_TEST_WORKER_ID;
+  const usageFile = process.env.WORKER_USAGE_FILE;
+  appendFileSync(usageFile, workerId + '\\n');
+});
+`,
+    );
+    testFiles.push(testFile);
+  }
+
+  const args = ['--test', '--test-concurrency=3', ...testFiles];
+  const result = spawnSync(process.execPath, args, {
+    env: { ...process.env, WORKER_USAGE_FILE: usageFile }
+  });
+
+  assert.strictEqual(result.status, 0, `Test failed: ${result.stderr.toString()}`);
+
+  // Read and analyze worker IDs used
+  const { readFileSync } = require('node:fs');
+  const workerIds = readFileSync(usageFile, 'utf8').trim().split('\n');
+
+  // Count occurrences of each worker ID
+  const workerCounts = {};
+  workerIds.forEach((id) => {
+    workerCounts[id] = (workerCounts[id] || 0) + 1;
+  });
+
+  const uniqueWorkers = Object.keys(workerCounts);
+  assert.strictEqual(
+    uniqueWorkers.length,
+    3,
+    `Should have exactly 3 unique worker IDs, got ${uniqueWorkers.length}: ${uniqueWorkers.join(', ')}`
+  );
+
+  Object.entries(workerCounts).forEach(([id, count]) => {
+    assert.strictEqual(count, 3, `Worker ID ${id} should be used 3 times, got ${count}`);
+  });
+});