Mechanisms are provided for identity mapping in synchronization systems. For example, entities can be mapped across various entity stores, such that an entity in one store can be identified with an entity in another store even if such entities are of different types. When entities are being synchronized across various entity stores, new or updated entity identities (and associated metadata) can be supplied to these stores as part of the same operation as that used for supplying changes during synchronization: entities can be merged and associated identity information and metadata can be changed accordingly; entities can be resurrected and new identity information can be created; metadata can be utilized even though entities are deleted, and so on.