Microservices architecture has become enormously popular because traditional monolithic architectures no longer meet the needs of scalability and rapid development cycle, and the success of some large companies in building and deploying services is a strong motivation for others to consider making the change. However, performing the migration process is not trivial. Most systems acquire too many dependencies between their modules, and thus can't be sensibly broken apart. It is for this reason that studies that provide information associated with the migration process to practitioners are necessary. This study gathers, organizes and analyzes 20 migration techniques proposed in the literature. Results show that most proposals use approaches based on design elements as input; 90% of the proposals were applied to object-oriented software (Java being the predominant programming language); And that the main challenge is to perform the database migration.