A multidatabase system (MDBS) is a collection of local database management system,each of which may follow a different concurrency control protocol. this heterogeneity makes the task of ensuring global serializability in an MDBS environment difficult. in this paper,we reduce the problem of ensuring global serializability to the problem of ensuring serializabililty in a centralized database system. we identify characteristic of the concurrency control problem in an MDBS environment, and additional requirements on concurrency control schemes for ensuring global serializability. we then develop a range of concurrency control schemes that ensure global serializability in an MDBS envinronment, and at the same time meet the requirements. finally, we study the tradeoffs between the complexities of the various schemes and the degree of concurrency provided by each of them.