BEAST is a cross-platform software project for Bayesian analysis of molecular sequences and evolutionary processes. Its core program uses Markov chain Monte Carlo (MCMC) to evaluate rooted, time-calibrated phylogenies under strict or relaxed molecular clock models. By averaging across possible tree topologies in proportion to their posterior probability, BEAST supports both phylogenetic reconstruction and the testing of evolutionary hypotheses without relying on a single tree.

The BEAST X toolkit includes BEAUti, a graphical application for setting up standard analyses, alongside programs for examining and summarizing results. Its broader software collection includes Tracer, TreeTracer, TempEst, and tools for visualizing and processing evolutionary trees and data. BEAST also works with the BEAGLE high-performance computing library.

The project provides installation guidance, introductory and advanced tutorials, practical how-to guides, reference materials, and troubleshooting resources. These cover topics such as molecular clocks, phylogeography, phylodynamics, model selection, and analysis of large datasets. The documentation describes BEAST X version 10.5.0 and distinguishes it from BEAST2, an independent project.