Building green-field applications with Event Sourcing and CQRS is pretty well-understood today. Introducing these concepts into legacy application is a whole different story, however. The legacy database claims to be the source of truth, the language is polluted by technical terms used in existing systems, and developers are tempted to add more and more special cases to the existing software. This presentation condenses several years of experience from introducing Event Sourcing and CQRS into legacy applications (and minds), presenting deep insights into challenges, solutions, and attempted solutions. We will discuss what has worked, and what did not work.