In recent years, there has been an explosion in the use of rapid assays. In particular, the ease of use of lateral flow immunoassays has revolutionized the area of personal healthcare. Lateral flow immunoassay tests have become the format of choice for many testing situations such as pregnancy, ovulation, drug use (both therapeutic and illicit), infectious disease, environmental health, and even in the bio-defense and forensics markets. The key feature of a lateral flow test is that it is very simple for the end user. Normally, the user simply has to apply the sample and the test will run within a matter of minutes. In reality, the lateral flow test is a much more complicated medical device thanmany users appreciate.Within the plastic housing there can be five different membrane or fibrous components assembled onto a plastic backing. There are also at least two antibodies, an antibody conjugate, buffers, and blocking agents as well (see Chapters 4 and 8). Choosing the compatible solid phase materials and applying the biological components in a way that results in a sensitive and stable assay can be amajor challenge. For this reason, a new material termed FUSION 5 is designed to overcome many of these obstacles.