This volume provides an accessible and coherent introduction to some of the scientific progress on functional equations on groups in the last two decades. It presents the latest methods of treating the topic and contains new and transparent proofs. Its scope extends from the classical functional equations on the real line to those on groups, in particular, non-abelian groups. This volume presents, in careful detail, a number of illustrative examples like the cosine equation on the Heisenberg group and on the group SL(2, ℝ). Some of the examples are not even seen in existing monographs. Thus, it is an essential source of reference for further investigations.Contents:IntroductionAround the Additive Cauchy EquationThe Multiplicative Cauchy EquationAddition and Subtraction FormulasLevi–Civita's Functional EquationThe Symmetrized Sine Addition FormulaEquations with Symmetric Right Hand SideThe Pre-d'Alembert Functional EquationD'Alembert's Functional EquationD'Alembert's Long Functional EquationWilson's Functional EquationJensen's Functional EquationThe Quadratic Functional EquationK-Spherical FunctionsThe Sine Functional EquationThe Cocycle EquationAppendices:Basic Terminology and ResultsSubstitutes for CommutativityThe Casorati DeterminantRegularityMatrix-Coefficients of RepresentationsThe Small Dimension LemmaGroup CohomologyReadership: Advanced undergraduates, graduates and professional mathematicians interested in harmonic analysis and/or functional equations.