Bayesian Evolutionary Analysis Sampling Trees 2 (BEAST2) is a program for Bayesian phylogenetic and evolutionary analysis of molecular sequences data. It uses Markov chain Monte Carlo (MCMC) methods to average over tree space, allowing researchers to infer how species or viruses are related and how they have evolved over time. BEAST2 supports a wide range of models for molecular evolution, population dynamics, and phylodynamics, and is widely used in computational biology, epidemiology, and evolutionary research for reconstructing time-calibrated phylogenies.