In our first course on statistical mechanics, we learn that small subsystems equilibrate to the temperature of their surroundings. Surprisingly, their is another option. There are Hamiltonian's, called many-body localized, whose subsystems don't equilibrate even at infinite "temperature." In this talk, I will unpack these statements and explain how quantum circuits and entanglement give us a lens through which we can understand this phenomena. I will then show how we should start thinking about the transition between the many-body localized phase and the more canonical ergodic phase.