The nitrogen-vacancy (NV) center is a point defect in the dimond lattice. It consists of a nearest-neighbor pair of a nitrogen atom, which substitutes for a carbon atom, and a lattice vacancy. Its most explored and useful property is photoluminescense, which can be detected optically or plasmonically from an individual NV center, especially those in the negative charge state (NV−). Electron spins at NV centers, localized at atomic scales, can be manipulated at room temperature by applying a static magnetic field as well as microwave radiation. Here, different designs of microwave sources for NV centers spin manipulation will be presented and discussed.