Object-oriented application development is today in a state analogous to that of relational technology in the late '70s. The models are well understood, development tools are available, and prices are becoming attractive. However, most users have not yet reengineered their development methodologies and processes to accommodate object-oriented techniques in a way that can guarantee success in terms of time-to-market, costs, and quality. For more than 10 years, GTE has been working to reengineer user development methodologies and process so that object-oriented application development will be feasible — and repeatable — for large applications. This article reports on lessons learned from our experiences over a ten-year period in which three different teams developed three different applications of one-million lines of code or more. Some of these lessons were learned through near failures; others through difficult successes.