Historically, it hasn't always been easy to properly link Google Analytics and AdWords accounts together. It always had to be done from the same authoritative user.
For agencies, this was sometimes particularly difficult as they would be tasked with creating the link between the accounts, but didn't always have access to the original accounts. And for agencies that ran Analytics and/or AdWords accounts for multiple clients, this became even more challenging.
That changed last week as Google Analytics announced new method to allow users to link multiple Analytics and AdWords account using a simplified interface. You merely need to check a box next the accounts you want to link and go.
The new "bulk linking" process streamlines what needs to be done to link accounts between AdWords and Analytics. Previously, accounts were linked at the account level. With this new feature, AdWords accounts are now linked at the property level.
This also means that account owners don't need to give up their password to link accounts. Anyone with Edit permission at the property level can create and update links between AdWords and Analytics accounts.
The new linking feature isn't live for all users yet. But you'll be sure to see it in the upcoming weeks.
To find the new linking process, log into your Analytics account and go to the Admin area from the gray top menu. Look in the Property column and you'll find AdWords Linking.