Magnetic force microscopy (MFM) is an important advance in atomic force microscopy that opened up the study of submicrometer magnetic domains. The technique has especially found a central place in the magnetic data storage industry, i.e., in the imaging of magnetic media and devices, whether in the analysis of magnetically recorded bits or in the performance of transducers that read/write them. MFM is also used in fundamental research of magnetic materials and composites, from nanoparticles and nanowires to ferritin proteins. More recently, MFM has been used in tandem with piezoelectric force microscopy (PFM) to characterize multiferroic composites that exhibit magnetoelectric coupling. These composites that consist of both magnetorestrictive and piezoelectric components can also be characterized by operating PFM under an applied in-plane magnetic field using a variable field module (VFM). Research on these novel magnetic materials is driven by the search for higher-density data storage media, high-speed, low-power spintronic devices for computing, and a new class of dual electric-field- and magnetic-field-tunable signal-processing devices.