Asthma is a heterogeneous disorder with a complex etiology. Prevalence rates for asthma have been increasing in many countries over the past few decades. While it is unclear why this increase is occurring, the variation reported in asthma prevalence and severity associated with ethnicity offers some insight into the determinants of asthma. In this chapter, we discuss the data linking asthma to ethnicity and some of the factors that may explain this association. These include socioeconomic status, environmental exposures, the host microbiome, and genetics. A better understanding of these processes may inform future mechanistic studies and identify modifiable risk factors for targeted health care interventions.