This cluster of papers focuses on the diagnosis, treatment, and epidemiology of nontuberculous mycobacterial diseases, with a particular emphasis on Mycobacterium avium and Mycobacterium abscessus. It covers topics such as the impact of genotypic studies, antibiotic resistance, prevalence in specific patient populations (e.g., Crohn's disease, cystic fibrosis), and environmental sources. The cluster also delves into genomic and comparative genomic studies supporting the division of the genus Mycobacterium.