The Alloy Theoretic Automated Toolkit (ATAT) by the van de Walle group is a software package to perform thermodynamics calculations in ordered and disordered multicomponent alloys, including vibrational and configurational free energy contributions. It implements the cluster expansion and the Special Quasirandom Structures formalisms, lattice Monte Carlo simulations, lattice dynamics calculations and provides numerous conversion utilities. It is freely distributed and interfaces with VASP.