Laser-ablation split-stream (LASS) analysis—high-speed, high spatial-resolution, simultaneous isotopic and elemental analysis—enables petrochronology at a new level, through the interpretation of isotopic dates combined with elemental abundances and/or isotopic tracers. This contribution begins with an introduction to petrochronology, presents a new LASS technique using dual multi-collector–single-collector inductively-coupled plasma mass spectrometry, and offers examples of how this technique is used to decipher the evolution of rocks with complex geologic histories.