Magnetism has a long history in science and engineering. It has enabled economic and technical advancement from the compass, more than 2,000 years ago, to contemporary spintronic devices. While miniaturized magnetic transducers have been central to data storage and sensor devices, they have recently penetrated new areas including life sciences and biomedical applications. Miniaturized magnetic biodevices feature high performance, while at the same time they have the potential to reduce costs associated with healthcare, opening the door to a multi-billion dollar market. For example, magnetic microsystems combined with magnetic nanoparticles can facilitate highly sensitive diagnostic tools capable of early disease detection and point-of-care diagnostics. Magnetic nanotechnology also provides the means for controlled drug delivery and effective cancer treatment with minimal side effects. The last few years have seen tremendous developments in the field of spintronics by exploiting the interaction of spin-polarized currents and magnetic nanostructures. This talk will cover principles and examples of magnetic micro- and nanosystems, with an emphasis on the research being conducted at the Sensing, Magnetism, and Microsystems group at KAUST.