The purpose of a Lessons Learned Library is to capture and share actionable learnings from marketing initiatives. While the framework here illustrates a ‘lesson learned’ from a single initiative, the real value comes from organizing a growing number of lessons in a structured and centralized way. A Lessons Learned Library can become an increasingly valuable resource for marketers to refer to when planning new initiatives. Lessons can be captured when initiatives or experiments end (as part of a Retrospective or Post-Mortem Meeting), or when issues unexpectedly arise. Marketing teams need to have the discipline and structure in place to capture and codify lessons consistently as part of their regular operations.