Mold fungi are both useful and harmful. This book provides a comprehensive overview of the good and bad sides of mold fungi. After a definition and introduction to the topic of mold fungi, the authors discuss their biology, physiology, and genetics. Furthermore, the use of mold fungi in biotechnology, food production, and biological pest control is examined. The chapter on harmful effects and control addresses the negative impacts of mold as a pathogen in plants, animals, and humans, as well as the destructive power of mold fungi on various materials. This non-fiction book is aimed at students of life sciences as well as non-specialist readers who, due to their profession, deal with the effects of mold fungi. Additionally, the book is intended to engage interested laypersons.