<p>Monoclonal gammopathy of clinical significance (MGCS) is a general term that encompasses a spectrum of non-malignant clinical disorders that are directly caused by monoclonal immunoglobulins (monoclonal proteins) produced by clonal plasma cell proliferative disorders. It is best considered as a collection of specific disorders that represent non-malignant progression of monoclonal gammopathy of undetermined significance (MGUS). This review provides a comprehensive overview of MGCS, highlighting its pathophysiology, diagnostic approach, clinical manifestations, and current management strategies across multiple organ systems. The spectrum of MGCS includes specific renal, neurological, cutaneous, hematological, and ocular diseases, as well as multisystem disorders such as POEMS syndrome, Schnitzler syndrome, cryoglobulinemia, and TEMPI syndrome. The diagnosis of MGCS is often challenging as it requires establishing a causal link between a monoclonal protein and the specific disease entity or clinical manifestation. Treatment strategies vary by disease and target the underlying monoclonal protein-producing clone or are directed to limit the effects of the monoclonal protein. As clinical trials remain limited, current management relies on mechanistic insights and observational studies. Increased awareness of MGCS and its organ-specific clinical features is crucial for providing timely diagnosis and delivering targeted interventions that may reverse or halt disease progression.</p>