The objective of this paper is to identify suitable generator concepts for direct-drive wind turbines by reviewing direct-drive and geared generator systems. Usually, in literature, comparison of different generator systems is discussed with the criteria based on the energy yield, cost, and weight. Because direct-drive permanent-magnet machines are more superior in terms of the energy yield, reliability and maintenance problem, different promising permanent-magnet machines proposed in literature are also discussed to find suitable generator type. Finally, suitable concepts to overcome the disadvantages of direct-drive are suggested considering both electromagnetic and mechanical structure.