The prevalence of rheumatoid arthritis (RA) is relatively constant at 0.5–1.0% in many populations, but varies significantly between ethnic groups. Native American populations have the highest prevalence, while populations from China and Japan have very low occurrences. Genetic factors play a significant role in RA, with the HLA DRB1 alleles being the primary genetic risk factor. The strongest susceptibility factor is HLA DRB1*0404. Other genetic factors include tumor necrosis factor alleles and non-MHC genes such as corticotrophin-releasing hormone, oestrogen synthase, and cytokines. Environmental factors, such as female sex hormones, infection, and cigarette smoking, also influence RA risk. Oral contraceptive use and pregnancy are associated with a reduced risk, while breastfeeding after the first pregnancy increases the risk. Infection, particularly with Epstein-Barr virus, parvovirus, and certain bacteria, may trigger RA, but the evidence is inconclusive. Recent studies suggest a link between cigarette smoking and an increased risk of RA. Overall, the genetic and environmental factors contributing to RA are complex and require further research to fully understand their interactions.The prevalence of rheumatoid arthritis (RA) is relatively constant at 0.5–1.0% in many populations, but varies significantly between ethnic groups. Native American populations have the highest prevalence, while populations from China and Japan have very low occurrences. Genetic factors play a significant role in RA, with the HLA DRB1 alleles being the primary genetic risk factor. The strongest susceptibility factor is HLA DRB1*0404. Other genetic factors include tumor necrosis factor alleles and non-MHC genes such as corticotrophin-releasing hormone, oestrogen synthase, and cytokines. Environmental factors, such as female sex hormones, infection, and cigarette smoking, also influence RA risk. Oral contraceptive use and pregnancy are associated with a reduced risk, while breastfeeding after the first pregnancy increases the risk. Infection, particularly with Epstein-Barr virus, parvovirus, and certain bacteria, may trigger RA, but the evidence is inconclusive. Recent studies suggest a link between cigarette smoking and an increased risk of RA. Overall, the genetic and environmental factors contributing to RA are complex and require further research to fully understand their interactions.