In the ELISA format(s), the capture antibody is usually affixed to a solid phase, commonly referred to as the immunosorbent. How to tether the antibody most effectively will depend upon the physical properties of the support (plate well, latex bead, flow cell, etc.) as well as its chemical nature (hydrophobic, hydrophilic, the presence of reactive groups such as epoxide, etc.). Of course, it is ultimately the suitability of the antibody to withstand the linking process while preserving its antigen-binding efficiency that must be determined. In this chapter, the antibody immobilization processes and their consequences are described.