Amongst the plethora of affinity biosensor systems based on biomolecular recognition and labeling assays, magnetic labeling and detection has emerged as a promising approach. Magnetic labels can be detected by a wide range of non-invasive methods, are physically and chemically stable, relatively inexpensive to produce, and can be easily made biocompatible. Over a decade ago, the U. S. Naval Research Laboratory pioneered the use of giant magnetoresistive (GMR) sensors to detect biomolecules labeled with paramagnetic microbeads. Since then, our various investigations and engineering efforts have resulted in significant improvements in both the magnetoelectronic instrumentation and the assays associated with these magnetic labels. This paper and subsequent presentation provides a synopsis of the development of our technology which has evolved into a highly sensitive detection method.