The immobilization of biomolecules is an important technique for bio-analysis, and can be applied to biosensors with both high selectivity and high sensitivity. Many researchers have developed immobilization techniques to optimize these characteristics. In the last two decades, an immobilization technique that meets the desired requirements was developed by using polyelectrolytes to form complexes, based on the electrostatic binding between polycations and polyanions. This review summarizes the techniques used for the immobilization of biomolecules by polyelectrolyte complexes; it also discusses related subjects.