Fueled by the ever increasing data density in magnetic storage and the need for a better understanding of the physical properties of magnetic nanostructures there exists a strong demand for high-resolution magnetically sensitive microscopy techniques. The technique with the highest available resolution is spin-polarized scanning tunneling microscopy (SP-STM) which combines the atomic-resolution capability of conventional STM with spin-sensitivity. Beyond the investigation of ferromagnetic surfaces, thin films, and epitaxial nanostructures with unforeseen precision, it also allows the achievement of a long standing dream, i.e. the real space imaging of atomic spins in antiferromagnetic surfaces. The talk addresses a wide variety of phenomena in surface magnetism which in most cases could not be imaged directly before the advent of SP-STM. After starting with a brief introduction to basics of the contrast mechanism, I will present recent major achievements, like the direct observation of the atomic spin structure of domain walls in antiferromagnets and the visualization of thermally driven switching events in superparamagnetic particles consisting of a few hundreds atoms only. To conclude, I will describe the observation of complex spin structures containing 15 or more atoms.