I will discuss an invariant of singularities that plays an important role in birational geometry, the log canonical threshold. Depending on the time available, I plan to cover some of the following topics: 1) Definition and examples. Connection with multiplier ideals and vanishing theorems 2) Shokurov's ACC conjecture, and its connection with Termination of Flips 3) A proof of the conjecture on ambient smooth varieties 4) Asymptotic invariants for graded sequences of ideals 5) Connection with invariants in positive characteristic defined via Frobenius