This book is written in the interest of post-graduate students in Chemistry and Pharmaceutical Science who are looking at the research field, especially in the Medicinal Chemistry area. Medicinal Chemistry is the interdisciplinary subject which is a combination of Chemistry, Pharmacy, and Chemical Biology. The effort has been made to create interest and knowledge about the five-membered sulfur and nitrogen heterocyclic compounds of pharmacological importance with their physical properties and chemical reactivities. Thiophene, thiazole, and thiadiazole derivatives are having much importance in the field of drug discovery research. A detailed literature search has been made and presented in this book.