When we work with clients who have set up their own Google Adwords accounts, we like to link ourselves to them. This way we can log in and see their settings, reports and data for ourselves.
The trouble is, it’s not intuative as to how to go about creating this link. In Google Analytics the site owner goes into their account and simply adds us as a User. All they need to know to do this is our Google Account Login Name.
For Google Adwords, it’s the other way around. We have to ask to be linked to them. And the Login details are not what’s needed. The Client ID is the key!
So, if we’re the consultants, we ask the client to provide us with their ID.
This appears in the top right of their Adwords account screen.
And it’s in the format 123-123-1234
Once we know that, we can simply click on the link ‘Link Existing Account’ that appears in the top left of the list under the tab ‘My Client Centre’.

Linking to an existing Google Adwords account
If you would like to see how Google describe this process, then here is the relevant page from their help:
http://bit.ly/1hIG8C