Dermatomyositis (DM) is a complex, systemic autoimmune disease characterized by hallmark cutaneous manifestations and inflammatory myopathy. It is associated with significant morbidity due to multisystem organ involvement and a well-established risk of underlying malignancy. This review provides a comprehensive update on the integrated pathophysiology, clinical subtypes, diagnostic strategies, and current management of DM, with a special emphasis on the modern, serology-driven approach to patient care. The pathogenesis is understood as an immune-mediated microangiopathy, with a central role for the type I interferon signaling pathway in driving tissue damage in both skin and muscle. The classification of DM has evolved beyond clinical presentation to a clinico-serological model where myositis-specific autoantibodies define distinct phenotypes with critical prognostic implications. For instance, anti-TIF1γ and anti-NXP2 antibodies are strongly associated with a high risk of malignancy, while anti-MDA5 antibodies identify patients at high risk for rapidly progressive interstitial lung disease. The diagnostic approach integrates clinical findings with serological profiling, imaging studies such as muscle MRI, and histopathology, while a risk-stratified cancer screening protocol is a mandatory component of initial management in adults. Treatment has advanced from a primary reliance on corticosteroids and conventional immunosuppressants to include targeted therapies, such as rituximab and, more recently, Janus kinase inhibitors, which have shown efficacy in treating refractory disease. Ultimately, a personalized and multidisciplinary approach, guided by the patient's specific autoantibody profile, is essential for optimizing long-term outcomes in this heterogeneous disease.