The objectives of Category II and III Test Programs, particularly with relation to reliability demonstration, are described. Data is presented and analyzed from the Category II and III tests of two different systems, one a missile, the other an airborne radar fire control system. Examples are given of reliability improvements that were introduced during the Programs, with emphasis on coordination between factory and field. The importance of proper organization and control of the Test Program is discussed, and attendant problems are illustrated. It is concluded that even though limitations exist, Category II and III tests come the closest to allowing the total system to be exercised under operational conditions; and that from the test results, assessments can be made of demonstrated reliability, and significant reliability improvements can be achieved.