Costa Tsonopoulos was a thermodynamicist with great contributions in applied thermodynamics but also a passion and dedication in using thermodynamics in industrial practice. He is well-known for his widely used methods for estimating the second virial coefficients, but his interests and developments are much wider. They include, among others, experimental measurements for water-hydrocarbons phase equilibrium and many studies on equations of state, especially the cubic equations of state and his conviction on the great role such “rather simple” models play in chemical engineering. “In our opinion cubic EoS are here to stay”, he said together with Jack Heidman in 1985. Many decades later, this is still very much true. This manuscript presents a review of Costa Tsonopoulos work related to (cubic and other) equations of state with some contemporary remarks as well as results of two case studies from the petroleum and chemical industries where indeed we may need to go “beyond” cubic equations, but in a controlled and well-balanced fashion.