As monolithic systems become too large to deal with, many enterprises are drawn to breaking them down into the microservices architectural style. It is a worthwhile journey, but not an easy one. We've learned that to do this well, we need to start with a simple service, but then draw out services that are based on vertical capabilities that are important to the business and subject to frequent change. These services should be large at first and preferably not dependent upon the remaining monolith. We should ensure that each step of migration represents an atomic improvement to the overall architecture.