Abstract. This article explores the complex pathophysiology of autoimmune diseases with a primary focus on the mechanisms underlying the breakdown of immune tolerance. Immune tolerance is essential for preventing the immune system from attacking the body’s own tissues. The review covers both central and peripheral tolerance processes, highlighting how genetic predispositions, environmental factors, and immune regulatory failures contribute to the development of autoimmunity. Key cellular players, such as regulatory T cells and antigen-presenting cells, are discussed in relation to their roles in maintaining immune homeostasis. Additionally, the article examines current understanding of molecular mimicry, epitope spreading, and other pathogenic mechanisms leading to self-reactivity. The challenges in diagnosis and treatment of autoimmune diseases are also addressed, emphasizing the need for targeted therapeutic approaches aimed at restoring immune tolerance rather than merely suppressing immune responses.