Over the past few decades, spin detection and manipulation at the atomic scale using scanning tunneling microcopy has matured, which has opened the possibility of realizing spin-based functional devices with single atoms and molecules. This article reviews the principle of spin polarized scanning tunneling microscopy and inelastic tunneling spectroscopy, which are used to measure the static spin structure and dynamic spin excitation, respectively. Recent progress will be presented, including complex spin structure, magnetization of single atoms and molecules, as well as spin excitation of single atoms, clusters, and molecules. Finally, progress in the use of spin polarized tunneling current to manipulate an atomic magnet is discussed.