The reliable identification of compounds such as illegal growth promoters in animal or human is generally based on expensive gas chromatography-mass spectrophotometry analysis, a method that does not allow on a large-scale screening. The use of simple, semi-quantitative electrochemical biosensors may provide a means of screening for the presence of compounds such as illegal growth promoters (ie. steroids). A detail development of such kind of Bio/immunosensor has been described in the first three chapters of this book. Four and fifth chapter of this book investigated a comparative study on the use of a glassy carbon, screen printed carbon and carbon fibre as sensor material to detect p-aminophenol. This book will be an important collection for a University student, early stage researchers, advanced level researchers and veterinary scientist who are working in the area of Bioscience or Biotechnology.