The correctness of nested transactions for multidatabases differs from that of flat transactions in that, for nested transactions the execution order of siblings at each related site should also be consistent. In this paper we first propose a simple but powerful theory for the serializability of nested transactions in multidatabases and then a technique called Nested Tickets Method for Nested transactions (NTNT). The NTNT technique provides correctness of nested transactions in multidatabases without violating the local autonomy of the participating DBMSs. The algorithm is fully distributed, in other words there is no central scheduler. The correctness of the NTNT technique is proved by using the developed theory.