The paper presents an analysis of the performance of a doubly-fed induction generator (DFIG) at different modes of operations. The modes of operations of (DFIG) which depend on both the rotor speed and rotor-phasor voltage are investigated. An expression of a boundary slip which separate between motoring and generating operation is obtained. The electromagnetic torque and the flow of active and reactive power between the machine and the grid are investigated. Also, the characteristics of the stator power factor is investigated at different operating conditions.