Enzyme immunoassay and ELISA are important immunological tests for identification of antigen or antibody to diagnose different disease conditions. ELISA and blot techniques are important for diagnosis of hepatitis panel, HIV-AIDS and antigen- antibody reactions. Rapid Immunochromatographic Test (ICT) is very useful for rapid diagnosis of malaria, Kala-azar, TB etc. This chapter describes characteristics of EIA, ELISA and blot techniques. Different types of ELISA like-competitive, sandwich, rapid one step ELISA and different types of blot test like- southern, northern and western blots are described with principles and methods.