BCS theory of conventional superconductivity describes pairing of spin-singlet time-reversed states, and is characterized by an order parameter which breaks U(1)-gauge symmetry leading to basic superconducting properties, such as the Meissner effect, persistent current and flux quantization. By contrast, unconventional superconductors exhibit additional broken symmetries, which often lead to distinct superconducting phases with unique properties. In this talk I will survey current searches for time reversal symmetry breaking (TRSB) in unconventional superconductors. After a brief discussion on the origin of TRSB in condensed matter systems I will introduce various ways to detect such effects, and in particular the use of magneto-optic like measurements that utilize the Sagnac interferometer that was invented in our group. I will show results on a variety of unconventional superconductors and discuss their implications to the determination of the possible pairing symmetry in each system.