Abstract: Potential appliations of spin polarized scanning tunneling microscopy and spectroscopy(SP STM/S) are described. We show that SPSTM enables us to measure surface magnetic structure with atomic resolution and is much more sensitive than other magnetic microscopy techniques, while SPSTS allows spatially resolved mapping of domain structures and reveals the exchange split surface states of many kinds of surfaces. Furthermore,SP STM/S can be applied to study spin injection into semiconductors.