Immunoassays are introduced in this book in a very sophisticated and concise manner. From the elementary in vitro analysis of a particular biomolecule to the diagnosis or prognosis of a particular disease, one of the most broadly practiced technologies is immunoassays. With the help of a particular antibody to identify the biomolecule of interest, comparatively high specificity can be attained by immunoassays, so that complex biofluids (e.g. serum, urine, etc.) can be examined directly. Along with the binding specificity, the other essential characteristics of immunoassays are relatively high sensitivity for the detection of antibody-antigen complexes, and a broad dynamic spectrum for quantitation. This book targets some of the recent technologies for the advancement of new immunoassays which, over the past decade, have continued to grow aggressively in their advancement and applications.