A steroid is an organic molecule having four rings organized in a specific molecular configuration that is biologically active. Steroids serve two principal biological functions. First, they are important components of cell membranes that affect membrane fluidity. Second, they act as signaling molecules. Animals, plants, and fungi all contain hundreds of steroids. Steroid hormones influence metabolism and the biological processes. These hormones affect endocrine functions such as sexual differentiation and reproductive life. The pharmaceutical industry has used steroids for making anticancer, anti-inflammatories, anticonvulsants, contraceptives, and fertility drugs. Steroid dimers are a class of chemicals that are produced by a variety of marine creatures and can also be manufactured in laboratories. This class of compounds has a wide range of pharmacological and biological properties, and can be utilized to make molecular umbrellas for drug delivery. This book explores all the important aspects of steroids in the present-day scenario. It is a valuable compilation of topics, encompassing their chemistry as well as applications in drug design and delivery. This book is a vital tool for all researching or studying steroids.