The discovery of the giant magnetoresistance (GMR) effect has stimulated significant progress both in the theory of electronic transport in metallic layered structures and in biomedical and industrial applications. In this chapter, we will introduce the underlying mechanisms of the GMR effect, followed by several industrial and biomedical applications of GMR devices reported so far. GMR sensor surface modifications, sensors combined with different auxiliary tools such as microfluidic channels and magnetic flux concentrators (MFCs), are also introduced. The purposes of these auxiliary tools are to improve the detectivity of GMR field sensors and to confine and manipulate sub‐microliter volume of biological fluids for on chip bioassays. Different biomedical and industrial applications based on GMR sensors are reviewed. In biomedical applications, GMR biosensors are actively used for immunoassays, genotyping, biological field recording such as magnetoencephalography (MEG) and magnetocardiography (MCG), as well as food and drug safety supervision. For industrial applications, in addition to read/write heads in hard disk drives, GMR sensors are also reported for position and current sensing as well as material defect inspections.