Aggregate Production Planning (APP) is considered as an important stage in production systems, since it links operations with strategies and plays a key role in enterprise resource planning and organizational integration. An effective APP should not only provide the minimization of production and inventory costs, but also increase the level of service available to the customers. When maintaining APP, some of cost and demand parameters cannot be frequently determined as crisp values. Fuzzy logic is utilized in many engineering applications so as to handle imprecise data. This chapter provides a mathematical programming framework for aggregate production planning problem under imprecise data environment. After providing background information about APP problem, together with fuzzy linear programming, the fuzzy linear programming model of APP is solved on an illustrative example for different alpha-cut values.