First published in 2004, this book collects several up-to-date methods for quantitative analysis of biospecific interactions, a field that has a long history that perhaps can be said to have begun with the classical paper of G. Scatchard in 1949 (The attractions of proteins for small molecules and ions, but which has advanced impressively during the last few years. A precise spatial arrangement of just a few hydrogen bonds can confer a remarkably specific reversible association between two molecules. A web of weak interactions governs biospecific recognition in general. The binding equilibria in living cells tune and coordinate a multitude of functions. The thermodynamic properties of such interactions are often studied by binding experiments in simplified and essentially ideal systems. However, similar types of studies may elucidate the biologically relevant dynamic steady-state conditions in living cells and organisms, allowing for the very wide range of interactant concentrations and the interplay between the many reactions and interactions. The development in biosciences will continue with in-depth studies of macromolecules and membranes. More detailed knowledge will allow analyses of delicate balances between substances and events in the complex systems involved in life processes. Methods to study biospecific affinities are thus highly important tools for understanding mechanisms and effects of molecular binding events in vivo and in vitro, e.g., in biochemical, biomedical and pharmaceutical research, and for biotechnological research and production.