Thermodynamics is a science concerning the states of a system whether it is stable, metastable, unstable or any states between. In this presentation, the thermodynamic fundamentals are reviewed and discussed in terms of theory, modeling, and applications. It is demonstrated that CALPHAD (CALculations of PHAse Diagrams) method for modeling of thermodynamic properties of individual phases provides a mechanism to systematically model thermodynamics and other properties of multicomponent systems. The availability of first-principles calculations based on density functional theory has further significantly strengthened the CALPHAD approach, contributing to materials design and Materials Genome®, the improvement of modeling robustness, and the in-depth understanding of materials behaviors such as critical phenomena. Prof. Olson’s pinioning contributions in integrating computational thermodynamics and materials design will be discussed along with the author’s personal interactions with Prof. Olson over the years.