AdWords API v2009 allows closer feature parity with the AdWords Front-End. Starting from a clean slate also gave us the opportunity to reorganize the API to better expose the features added since v1. Here’re some changes:
-We've created new web services for managing campaign targeting options and campaign-level criteria
-All web services share a consistent, data-centric interface with two operations: get and mutate
-A secure authentication token replaces the login credentials required in v13 request headers.
More info: AdWords API v2009