Discussion of microservice architectures often emphasizes the transition from monolith to microservices. No less important, though, is the strategy for successfully evolving a microservice-based architecture over time. Change is inevitable, and assumptions made when microservice boundaries were initially drafted may no longer hold. Since changes at this stage often have real consequences, preventing architectural drift and the associated disorganization of services and responsibilities requires conscious effort and a willingness to take a holistic approach, with an equal focus on architecture, devops, and culture. N.Y.-based secondary ticketing marketplace SeatGeek marked its entrance into primary ticketing last year with the launch of SeatGeek Open. This was a major shift in strategy, and a number of fundamental assumptions about the core product, deeply ingrained in our microservice architecture, changed. Not least of all, we needed to integrate a monolithic component we had just paid $60MM to acquire. Managing the complexity of this evolution involved coordinated decisions about how to adjust existing services and incorporate new ones without harming our core money-making business. Using this experience as a backdrop, this talk will discuss the architectural, operational, and cultural aspects of evolving a microservice architecture, in the process highlighting both the opportunities and the challenges that microservice architectures present.