Classically if you have a particle in a double well potential as the one pictured on the right there is no trajectory for a particle to travel from one well to the other. Quantum mechanically, however, a particle can tunnel from one to the other -- these tunneling processes are described by Instantons . In this project you will see an alternative approach to quantum mechanics, called path integral quantization, that will make it easy to compute the tunneling probability. For that you will first recall Lagrangians, and study the principle of least action. Then, after getting acquainted with the path integral you will see instantons as classical solutions to the Euclidean equations of motion with a finite action, and study examples of instantons in quantum mechanics.