The book "Phase Diagrams and Heterogeneous Equilibria" offers a comprehensive introduction to the practical applications of phase diagrams, which are relevant for students of chemistry, metallurgy, mineralogy, and materials science, as well as for engineers and professionals in related fields. It covers the fundamental principles of heterogeneous equilibria, which have been known since the work of J.W. Gibbs in 1878. The content is structured to first address the reactions and dynamic equilibria that are familiar to the readers. Through clear explanations and practical examples, the formal approach to describing phase equilibria is made more accessible. The book aims to emphasize the necessity of understanding phase diagrams while also providing practical exercises to deepen knowledge.