The chapter describes the main diseases affecting hop, including their importance, damage, and characteristics, as well as their management using chemical, cultural, biological, or quarantine methods. It is divided into sections based on groups of causal agents, starting with the most extensive group, fungal, oomycete, and bacterial diseases. The emphasis is on major diseases such as downy mildew, powdery mildew, and verticillium wilt, as well as diseases that can cause significant damage to certain cultivars or may appear sporadically in different years or regions. The second section covers descriptions of the most important viruses and viroids infecting hop, along with the basic principles of their management. In both of the first two sections, there are brief descriptions of diseases of minor importance, including pathogens that are rarely reported on hop and that typically do not cause severe crop damage. The last two sections address nematode diseases and abiotic diseases caused by non-infectious factors such as nutrient disorders, environmental stress, and chemical injuries.