In this paper, the basic principles, schemes, characteristics and their recent developments and applications of magnetic traps are reviewed in detail. All these magnetic traps can be divided into three kinds: macroscopic static magnetic trap, microscopic static magnetic trap and microwave or ac magnetic trap, according to the sizes of magnetic-trap devices, the characteristics of magnetic wells and the methods of generating magnetic fields. Finally, some recent applications of magnetic traps in the experiments of Bose-Einstein condensation (BEC) and atomic chip are briefly introduced.