Primary systemic amyloidosis, or light chain (AL) amyloidosis, is a rare lymphoproliferative disorder in which aberrant light-chain immunoglobulins secreted into the bloodstream aggregate into fibrils and deposit into tissues, causing widespread organ damage and, if not treated, death. This review provides a comprehensive summary of the pathophysiology and manifestations of AL amyloidosis; standard-of-care diagnostic approach; typical treatment regimens; and areas of active investigation.