# SessionHeader

Specifies the session ID returned from the login server after a successful `login()`. This session ID is used in all subsequent calls.

In version 12.0 and later, include the API namespace in the SOAP message associated with this header. The namespace is defined in the enterprise or partner WSDL.

## API Calls

All calls, including utility calls.

## Fields

### `sessionId`

**Type:** string

**Description:** Session ID returned by the `login()` call to be used for subsequent call authentication.

## Sample Code

See the examples provided for [`login()`](https://developer.salesforce.com/docs/atlas.en-us.api.meta/api/sforce_api_calls_login.htm).