Autoimmune diseases such as rheumatoid arthritis (RA), type 1 diabetes (T1D), and multiple sclerosis (MS) arise from a complex interplay between genetic susceptibility and environmental triggers. While genetic predisposition lays the foundation for these diseases, environmental factors, such as infections, dietary habits, toxins, smoking, and UV radiation, play a critical role in disease initiation and progression. This chapter explores the mechanisms by which environmental factors influence immune dysregulation, leading to the breakdown of self-tolerance and chronic inflammation. Specific triggers, including viral and bacterial infections, pollutants, gut microbiome dysbiosis, and epigenetic modifications, are examined for their role in autoimmunity. Additionally, we discuss emerging preventive strategies, such as lifestyle modifications, early risk detection, and targeted therapies, which aim to mitigate environmental influences on autoimmune diseases. A deeper understanding of these interactions offers new therapeutic insights and avenues for disease prevention, emphasizing the need for personalized approaches to managing autoimmunity.