The importance of immunoassays for accurate and sensitive detection of various analytes is a proven fact in the area of clinical diagnosis. The development of immunoassays for any drug, hormone, hapten or large molecular weight protein needs an in-depth understanding of various parameters that may affect the assay function. Sensitivity and specificity are two of the main parameters that determine the success of any assay. The book focuses on investigating the effect of spacers in improving these parameters taking cortisol as model hapten. This book therefore, will add to the understanding of readers on how a successful immunoassay for haptens can be developed. Moreover, the book also encompasses the development of a rapid and semi-quantitative assay for cortisol which is user friendly and does not require any sophisticated equipment. The readers will be interested to find out the methodology of developing such a rapid assay which does need a well-established laboratory.