Summary: This paper considers the two-phase warranty models for repairable products. It defines the time-interval [\(0,W\)] as the first phase (warranty period) and the time interval (\(W,T+W\)) as the second phase (buyer survival period). The products have two types of failures: type I failures (minor failures) and type II failures (catastrophic failures). In the model, type I failures are also removed by minimal repairs in the first and the second phases, and type II failures are removed by replacements in the first phase. If type II failures take place in the second phase, then it is supposed the life of products will be ended. To buy a new product is conducted at time \(T+W\) or upon the type II failure. Whenever each replacement takes place, the spare unit is ordered and then delivered. Therefore, the lead-time is considered. This thesis considers three warranty and maintenance models for seller, buyer and the society. The objective is to obtain the optimal \(T^*\). Finally, a numerical example is provided.