Lichenology introduces the fundamental principles of lichenology, a branch of microbiology. Drawing on years of teaching experience at King Saud University, the book explores the structure, organization, and reproduction of lichens, as well as the functions of their organs and growth factors. It examines the impact of pollutants on lichens and reviews their economic importance and uses, supported by examples and images. The goal is to present the material engagingly to enhance students' academic achievement and efficiency in studying this science.