Superradiance occurs in a black hole spacetime when there is no globally defined Killing vector field which is non-spacelike both at the horizon of the black hole and the asymptotic region. In this case "energy" can leak out of the black hole possibly causing instabilities. In the first part of the talk I will review the Kerr spacetime with an emphasis on the role of superradiance. In the second part of the talk I will describe how superradiance allows one to construct finite energy exponentially growing solutions to the Klein-Gordon equation. Along the way I will attempt to discuss the moral implications of this linear instability.