As Feynman noted, rules of chemistry are determined “in principle” by physics, but just as knowing the rules of chess do not immediately make one a great chess player, deriving chemistry from physics has challenged scientists for the past century. To predict thermodynamic properties of matter depends on two branches of physics: quantum mechanics, which governs the energetics and dynamics of elementary constituent particles; statistical mechanics, which deals with interactions of many particles and introduces the concept of temperature. This talk surveys new developments in computational thermodynamics that allow prediction of alloy phase diagrams and crystal structures truly from first principles.