The successful conjunction of the ultimate spatial resolution capability of the scanning tunneling microscope (STM) with the sensitivity to the spin of the tunneling electrons has opened the door to investigations of magnetism at the nanoscale where the fundamental interactions responsible for magnetic order can be studied. Spin-polarized (SP) STM allows insight into a fascinating world with surprisingly rich magnetic phenomena. Ferromagnetic structures with magnetic domains are found at nanometer length scales, or 2D antiferromagnetically ordered monolayers (MLs) where the magnetization is reversed from one atom to the next. Such collinearly ordered states may be modified by the Dzyaloshinsky-Moriya (DM) interaction which can induce a small canting angle between neighboring atomic moments, thus giving rise to novel non-collinear spin spiral ground states. DM interaction is a result of electron scattering in a crystal environment with broken inversion symmetry. Spin spirals were observed in a variety of systems, like ultrathin Fe films, or MLs of Mn atoms on the (110) and (001) faces of a W crystal. Using a magnetically sensitive probe tip, individual Co atoms were assembled to form chains on top of a spin spiral. The magnetization orientation of each individual atom can be manipulated by repositioning it along the spin spiral.