Modern alloys appear and develop as complex multi- component systems with the aim of accomplishing demands of metallurgical engineering, material science and industry. Nowadays, many commercial software systems can be found in the market to perform complicated calculations, in order to obtain thermodynamic properties of materials. This work reviews the algorithms, procedures, formulations and calculations behind the most common approach used in computational thermochemistry, CALPHAD (CALculation of PHAse Diagrams).