The timescales most commonly associated with tectonically driven metamorphism are typically in the millions to tens of millions of years. However, recent work has illuminated much shorter lived pulses of metamorphism that can exist, or even dominate, in natural systems. This seminar will review the building evidence for these pulses, quantify their characteristics, and begin to explain their significance. While several examples of metamorphic pulses will be reviewed spanning regional and subduction zone settings, this seminar will highlight the refinement and utilization of zoned garnet Sm-Nd geochronology to recognize pulses and put them into petro-tectonic context. Modern methods for zoned garnet Sm-Nd geochronology now permit chemically contoured microsampling and age analysis at <1 Ma temporal precision. Coupled geochronologic and thermodynamic data from regional (Scotland, Austria) and subduction zone (Sifnos, Greece) settings will be presented, revealing that metamorphic processes including heating and dehydration can operate very rapidly and over very short time intervals.