Fungi are eukaryotic microorganisms and can occur as yeasts, molds or as a combination of both forms. Mycology refers to the branch of biology involved in the study of fungi. It is concerned with the study of genetic and biochemical properties of fungi, as well as their taxonomy, benefits and harmful effects. There are three ways of classifying fungi based on their ability to reproduce asexually, sexually or by a combination of both. Fungi have several applications in a variety of industries such as food and pesticide. Yeast is a unicellular fungus used for making bread and other food items. The antibiotic known as penicillin is also obtained from a fungus named Penicillium notatum. This book provides significant information on fungi to help develop a good understanding of its diversity, ecology and biotechnological applications. It will also provide interesting topics for research which interested readers can take up.