For 25 years the NASA/GSFC Software Engineering Laboratory
(SEL) has been a major resource in software process
improvement activities. But due to a changing climate at NASA,
agency reorganization, and budget cuts, the SEL has lost much
of its impact. In this paper we describe the history of the SEL
and give some lessons learned on what we did right, what we did
wrong, and what others can learn from our experiences. We
briefly describe the research that was conducted by the SEL,
describe how we evolved our understanding of software process
improvement, and provide a set of lessons learned and
hypotheses that should enable future groups to learn from and
improve on our quarter century of experiences.