Work-related asthma is one of the principal occupational respiratory diseases in terms of prevalence. Innumerable chemical substances used in various production processes can cause or aggravate occupational asthma. This chapter contains a brief description of the definition and classification of work-related asthma, as well as the epidemiological repercussions, natural course, diagnostic criteria, progression and legal aspects of the disease, with the objective of raising an alert regarding this disease and its implications for workers.