Interaction between molecules is the basis for life in cells and higher organisms. Detailed investigations of the intimate relationship between the structural properties of interacting molecules and then biological function, and the biological consequences of their interactions are therefore central research topics in modern molecular biology. The molecular interactions referred to here can be of many types; for example, antibody—antigen, receptor—ligand, and DNA-protein. The above issues must generally be addressed on different levels of molecular complexity, including organisms, cells, proteins, and peptides, as well as low-mol-wt species like hormones, vitamins, ammo acids, sugars, and so forth, by employing a broad range of biochemically and biologically oriented methods and assays. Development of new technology with improved sensitivity, specificity, and speed is therefore exceedingly important in order to be able to meet the increasing demands from the molecular biologists.