The paper provides a comprehensive review of a wide range of problems and inconsistencies in current cost-effectiveness test practices, and recommends a range of best practices to address them. These best practices (a) align test implementation with the underlying objectives of the tests as originally designed;(b) ensure that energy resources are developed at the lowest cost; and (c) support public policy goals such as promoting customer equity, serving a broad range of customers, encouraging comprehensive whole-house improvements, and avoiding lost opportunities.