Now that Washington State has logged more than five years with a whole building air leakage testing requirement intended to demonstrate building air leakage performance, the local industry has had the unique opportunity to gain insight into building performance in aggregate, in a way that not many other building communities have. This experience has allowed designers, builders, and owners in our industry to digest the realities of the requirements, refine the testing processes, and learn lessons on different air barrier design approaches. As codes nationally continue to move in the direction of more stringent air barrier requirements, the authors of this paper have stepped back to discuss some insights gained through their experience testing a variety of projects, including numerous midrise, mixed-use, multifamily buildings in the Seattle, Washington, area. This paper will review the background of whole building air leakage testing in Washington State, and identify some of the challenges that have presented. We will touch on insights that the industry has gathered, as it pertains to testing sensitivities and common leakage paths. We will finish the discussion by looking at the testing standards and discussing potential revisions to these standards and processes to better align the tests with the intent that drives these requirements.