Heterocycles are an important class of compounds, making up more than half of all known organic compounds. They have been frequently found as a key structural units in synthetic chemistry. The book consists of the synthesis of different heterocyclic rings from the hydrazine or hydrazide derivatives. The book has also tried to cover the biological activities of these heterocyclic ring systems. The book is going to be of great help to the students of postgraduate as well as doctoral students.