This book aims at providing the concepts of topological indices and its applications in various fields. Topological indices capture the symmetry of molecular structure and provide a mathematical language to predict physical and chemical properties of chemical compounds. In the fields of chemical graph theory, molecular topology, and mathematical chemistry a topological index also known as a connectivity index. These topological indices are numerical parameters of a graph which characterize its topology and are usually graph invariant. Also, this book offers examples of topological indices in the development of quantitative structure-activity relationships and quantitative structure-property relationships (QSAR/QSPRs) in which the biological activity or other properties of molecules are correlated with their chemical structure.