In this talk, I will give an introduction to the so called mutation operation of a 3-manifold, which can be described as cutting the 3-manifold along a given surface and then sew it back in a different way. In particular, this induces corresponding mutation operations on knots obtained by mutating the 3-sphere along a genus 2 surface in the knot complement. I will survey a few properties and conjectures regarding mutant knots.