With each methodology treated in its own chapter, this monograph is a thorough exploration of several theories that can be used to find explicit formulas for heat kernels for both elliptic and sub-elliptic operators. The authors show how to find heat kernels for classical operators by employing a number of different methods. Some of these methods come from stochastic processes, others from quantum physics, and yet others are purely mathematical. What is new about this work is the sheer diversity of methods that are used to compute the heat kernels. It is interesting that such apparently distinct branches of mathematics, including stochastic processes, differential geometry, special functions, quantum mechanics and PDEs, all have a common concept – the heat kernel. This unifying concept, that brings together so many domains of mathematics, deserves dedicated study. Heat Kernels for Elliptic and Sub-elliptic Operators is an ideal resource for graduate students, researchers, and practitioners in pure and applied mathematics as well as theoretical physicists interested in understanding different ways of approaching evolution operators.