diff --git a/README.md b/README.md
index 6ca24460d..cdf9ba0dd 100644
--- a/README.md
+++ b/README.md
@@ -130,6 +130,29 @@ The session will have the name "GitHubActions" and be tagged with the following
 
 _Note: all tag values must conform to [the requirements](https://docs.aws.amazon.com/STS/latest/APIReference/API_Tag.html). Particularly, `GITHUB_WORKFLOW` will be truncated if it's too long. If `GITHUB_ACTOR` or `GITHUB_WORKFLOW` contain invalid charcters, the characters will be replaced with an '*'._
 
+## Self-hosted runners
+
+If you run your GitHub Actions in a [self-hosted runner](https://help.github.com/en/actions/hosting-your-own-runners/about-self-hosted-runners) that already has access to AWS credentials, such as an EC2 instance, then you do not need to provide IAM user access key credentials to this action.
+
+If no access key credentials are given in the action inputs, this action will use credentials from the runner environment using the [default methods for the AWS SDK for Javascript](https://docs.aws.amazon.com/sdk-for-javascript/v2/developer-guide/setting-credentials-node.html).
+
+You can use this action to simply configure the region and account ID in the environment, and then use the runner's credentials for all AWS API calls made by your Actions workflow:
+```yaml
+uses: aws-actions/configure-aws-credentials@v1
+with:
+  aws-region: us-east-2
+```
+In this case, your runner's credentials must have permissions to call any AWS APIs called by your Actions workflow.
+
+Or, you can use this action to assume a role, and then use the role credentials for all AWS API calls made by your Actions workflow:
+```yaml
+uses: aws-actions/configure-aws-credentials@v1
+with:
+  aws-region: us-east-2
+  role-to-assume: my-github-actions-role
+```
+In this case, your runner's credentials must have permissions to assume the role.
+
 ## License Summary
 
 This code is made available under the MIT license.
diff --git a/action.yml b/action.yml
index 96d305861..2e3b8f277 100644
--- a/action.yml
+++ b/action.yml
@@ -5,11 +5,17 @@ branding:
   color: 'orange'
 inputs:
   aws-access-key-id:
-    description: 'AWS Access Key ID'
-    required: true
+    description: >-
+      AWS Access Key ID. This input is required if running in the GitHub hosted environment.
+      It is optional if running in a self-hosted environment that already has AWS credentials,
+      for example on an EC2 instance.
+    required: false
   aws-secret-access-key:
-    description: 'AWS Secret Access Key'
-    required: true
+    description: >-
+      AWS Secret Access Key. This input is required if running in the GitHub hosted environment.
+      It is optional if running in a self-hosted environment that already has AWS credentials,
+      for example on an EC2 instance.
+    required: false
   aws-session-token:
     description: 'AWS Session Token'
     required: false
diff --git a/index.js b/index.js
index b24d1a20f..b4455d9c0 100644
--- a/index.js
+++ b/index.js
@@ -141,8 +141,8 @@ function getStsClient(region) {
 async function run() {
   try {
     // Get inputs
-    const accessKeyId = core.getInput('aws-access-key-id', { required: true });
-    const secretAccessKey = core.getInput('aws-secret-access-key', { required: true });
+    const accessKeyId = core.getInput('aws-access-key-id', { required: false });
+    const secretAccessKey = core.getInput('aws-secret-access-key', { required: false });
     const region = core.getInput('aws-region', { required: true });
     const sessionToken = core.getInput('aws-session-token', { required: false });
     const maskAccountId = core.getInput('mask-aws-account-id', { required: false });
@@ -151,13 +151,21 @@ async function run() {
     const roleDurationSeconds = core.getInput('role-duration-seconds', {required: false}) || MAX_ACTION_RUNTIME;
     const roleSessionName = core.getInput('role-session-name', { required: false }) || ROLE_SESSION_NAME;
 
+    exportRegion(region);
+
     // Always export the source credentials and account ID.
     // The STS client for calling AssumeRole pulls creds from the environment.
     // Plus, in the assume role case, if the AssumeRole call fails, we want
     // the source credentials and accound ID to already be masked as secrets
     // in any error messages.
-    exportRegion(region);
-    exportCredentials({accessKeyId, secretAccessKey, sessionToken});
+    if (accessKeyId) {
+      if (!secretAccessKey) {
+        throw new Error("'aws-secret-access-key' must be provided if 'aws-access-key-id' is provided");
+      }
+
+      exportCredentials({accessKeyId, secretAccessKey, sessionToken});
+    }
+
     const sourceAccountId = await exportAccountId(maskAccountId, region);
 
     // Get role credentials if configured to do so
diff --git a/index.test.js b/index.test.js
index 51c58ef73..f3f24aaa9 100644
--- a/index.test.js
+++ b/index.test.js
@@ -32,17 +32,17 @@ function mockGetInput(requestResponse) {
         return requestResponse[name]
     }
 }
-const REQUIRED_INPUTS = {
+const CREDS_INPUTS = {
     'aws-access-key-id': FAKE_ACCESS_KEY_ID,
     'aws-secret-access-key': FAKE_SECRET_ACCESS_KEY
 };
 const DEFAULT_INPUTS = {
-    ...REQUIRED_INPUTS,
+    ...CREDS_INPUTS,
     'aws-session-token': FAKE_SESSION_TOKEN,
     'aws-region': FAKE_REGION,
     'mask-aws-account-id': 'TRUE'
 };
-const ASSUME_ROLE_INPUTS = {...REQUIRED_INPUTS, 'role-to-assume': ROLE_ARN, 'aws-region': FAKE_REGION};
+const ASSUME_ROLE_INPUTS = {...CREDS_INPUTS, 'role-to-assume': ROLE_ARN, 'aws-region': FAKE_REGION};
 
 const mockStsCallerIdentity = jest.fn();
 const mockStsAssumeRole = jest.fn();
@@ -118,8 +118,24 @@ describe('Configure AWS Credentials', () => {
         expect(core.setSecret).toHaveBeenCalledWith(FAKE_ACCOUNT_ID);
     });
 
+    test('hosted runners can pull creds from a self-hosted environment', async () => {
+        const mockInputs = {'aws-region': FAKE_REGION};
+        core.getInput = jest
+            .fn()
+            .mockImplementation(mockGetInput(mockInputs));
+
+        await run();
+        expect(mockStsAssumeRole).toHaveBeenCalledTimes(0);
+        expect(core.exportVariable).toHaveBeenCalledTimes(2);
+        expect(core.setSecret).toHaveBeenCalledTimes(1);
+        expect(core.exportVariable).toHaveBeenCalledWith('AWS_DEFAULT_REGION', FAKE_REGION);
+        expect(core.exportVariable).toHaveBeenCalledWith('AWS_REGION', FAKE_REGION);
+        expect(core.setOutput).toHaveBeenCalledWith('aws-account-id', FAKE_ACCOUNT_ID);
+        expect(core.setSecret).toHaveBeenCalledWith(FAKE_ACCOUNT_ID);
+    });
+
     test('session token is optional', async () => {
-        const mockInputs = {...REQUIRED_INPUTS, 'aws-region': 'eu-west-1'};
+        const mockInputs = {...CREDS_INPUTS, 'aws-region': 'eu-west-1'};
         core.getInput = jest
             .fn()
             .mockImplementation(mockGetInput(mockInputs));
@@ -139,7 +155,7 @@ describe('Configure AWS Credentials', () => {
     });
 
     test('can opt out of masking account ID', async () => {
-        const mockInputs = {...REQUIRED_INPUTS, 'aws-region': 'us-east-1', 'mask-aws-account-id': 'false'};
+        const mockInputs = {...CREDS_INPUTS, 'aws-region': 'us-east-1', 'mask-aws-account-id': 'false'};
         core.getInput = jest
             .fn()
             .mockImplementation(mockGetInput(mockInputs));
@@ -218,6 +234,36 @@ describe('Configure AWS Credentials', () => {
         expect(core.setOutput).toHaveBeenNthCalledWith(2, 'aws-account-id', FAKE_ROLE_ACCOUNT_ID);
     });
 
+    test('assume role can pull source credentials from self-hosted environment', async () => {
+        core.getInput = jest
+            .fn()
+            .mockImplementation(mockGetInput({'role-to-assume': ROLE_ARN, 'aws-region': FAKE_REGION}));
+
+        await run();
+        expect(mockStsAssumeRole).toHaveBeenCalledTimes(1);
+        expect(core.exportVariable).toHaveBeenCalledTimes(5);
+        expect(core.setSecret).toHaveBeenCalledTimes(5);
+        expect(core.setOutput).toHaveBeenCalledTimes(2);
+
+        // first the source account is exported and masked
+        expect(core.setSecret).toHaveBeenNthCalledWith(1, FAKE_ACCOUNT_ID);
+        expect(core.exportVariable).toHaveBeenNthCalledWith(1, 'AWS_DEFAULT_REGION', FAKE_REGION);
+        expect(core.exportVariable).toHaveBeenNthCalledWith(2, 'AWS_REGION', FAKE_REGION);
+        expect(core.setOutput).toHaveBeenNthCalledWith(1, 'aws-account-id', FAKE_ACCOUNT_ID);
+
+        // then the role credentials are exported and masked
+        expect(core.setSecret).toHaveBeenNthCalledWith(2, FAKE_STS_ACCESS_KEY_ID);
+        expect(core.setSecret).toHaveBeenNthCalledWith(3, FAKE_STS_SECRET_ACCESS_KEY);
+        expect(core.setSecret).toHaveBeenNthCalledWith(4, FAKE_STS_SESSION_TOKEN);
+        expect(core.setSecret).toHaveBeenNthCalledWith(5, FAKE_ROLE_ACCOUNT_ID);
+
+        expect(core.exportVariable).toHaveBeenNthCalledWith(3, 'AWS_ACCESS_KEY_ID', FAKE_STS_ACCESS_KEY_ID);
+        expect(core.exportVariable).toHaveBeenNthCalledWith(4, 'AWS_SECRET_ACCESS_KEY', FAKE_STS_SECRET_ACCESS_KEY);
+        expect(core.exportVariable).toHaveBeenNthCalledWith(5, 'AWS_SESSION_TOKEN', FAKE_STS_SESSION_TOKEN);
+
+        expect(core.setOutput).toHaveBeenNthCalledWith(2, 'aws-account-id', FAKE_ROLE_ACCOUNT_ID);
+    });
+
     test('role assumption tags', async () => {
         core.getInput = jest
             .fn()
@@ -287,7 +333,7 @@ describe('Configure AWS Credentials', () => {
     test('role name provided instead of ARN', async () => {
         core.getInput = jest
             .fn()
-            .mockImplementation(mockGetInput({...REQUIRED_INPUTS, 'role-to-assume': ROLE_NAME, 'aws-region': FAKE_REGION}));
+            .mockImplementation(mockGetInput({...CREDS_INPUTS, 'role-to-assume': ROLE_NAME, 'aws-region': FAKE_REGION}));
 
         await run();
         expect(mockStsAssumeRole).toHaveBeenCalledWith({