We give an introduction to spin-polarized scanning tunneling microscopy (Sp- STM), a magnetic imaging technique with nanometer lateral resolution. Sp-STM allows to record constant current images which represent the electron density near the sample surface and simultaneously the spin polarization of the electron density which is related to the magnetic moment. It is shown how magnetic and topographic information can be separated using a modulation technique of the magnetization of bulk ferromagnetic tips. It is demonstrated that the out-of-plane component as well as one well-defined in-plane component of the spin polarization can be recorded. Finally, it is shown that with Sp-STM valuable information on the spin-resolved electronic structure and on the fundamental processes of tunneling spins may be obtained.