A harmonic drive (1), including a wave generator (8), a flexible, externally toothed gear component (14), in particular in the form of a flex ring, which can be deformed by said wave generator, and at least one internally toothed gear component (4, 5) that meshes with the flexible, externally toothed gear component (14). The flexible, externally toothed gear component (14) has a non-circular basic shape in relation to its mechanically non-loaded state.