Fungi are a diverse and fascinating group of organisms that play important roles in nature and human society. They can be found in almost every habitat and environment, from soil and water to plants and animals. They can also cause diseases, produce useful substances, or form symbiotic relationships with other organisms. To study and understand fungi, we need to classify them into different groups based on their characteristics and relationships. One of the most widely used classifications of fungi was proposed by C. J. Alexopoulos and C. W. Mims in 1979. In this article, we will explore the classification of fungi by Alexopoulos and Mims, its features, advantages, and limitations. We will also provide a free PDF resource that contains a detailed overview of the classification system and examples of each group of fungi.