This chapter examines what areas of science are needed to allow optimal use of ELISA and notes their relationships. This information is useful for students and those instructing students. Diagrams, with brief descriptions of key points, are used to illustrate such relationships. Inherent in this exercise are considerations of the exact requirements by the operators in using the ELISA. Attention to increasing knowledge in those areas highlighted is essential both in developmental work to produce a working ELISA and in the ultimate value of any test devised. A good deal of attention should be directed at defining, as clearly as possible, the objectives for the ELISA. The development of a diagnostic test for a specific disease requires that all other data pertaining to the biology of that disease, e.g., antigenicity and structure of the agent, antibody production in different animals following infection, qualitative assessment of antibodies by different assays, and availability of standard or control sera, are known. Some attention must be paid to the laboratory facilities available, e.g., equipment, reagents already developed, small laboratory animals, experimental large animals, cash to buy commercial products, and trained personnel. In this way, the chances of producing a sustainable test to solve the defined problem are significantly greater than when a test is developed by a dabbling technique with poor or no forward planning.