Introduction: Inflammation underlies the pathogenesis of numerous neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). In ALS, the complement system has been implicated in the neuropathology of disease and disease progression. Pegcetacoplan, a subcutaneously administered C3 complement inhibitor, is being investigated in hematology, nephrology, and neurology. The current clinical study (NCT04579666) is investigating whether pegcetacoplan can improve survival and function in people diagnosed with apparent sporadic ALS. Objectives and Methodology: Evaluate the efficacy and safety of pegcetacoplan compared to placebo among people diagnosed with ALS in a global, multicenter, randomized, double-blind, placebo-controlled, phase 2 study. Approximately 228 patients diagnosed with apparent sporadic ALS, ≥18 years of age and with an ALS Functional Rating Scale-Revised (ALSFRS-R) score ≥30, slow vital capacity (SVC) ≥60% of the predicted value at screening, and with symptom onset within 72 weeks before screening, are eligible for enrollment. After screening, patients will be randomized 2:1 to treatment groups receiving either subcutaneous pegcetacoplan (1080 mg) or placebo twice weekly for a duration of 52 weeks. The primary efficacy endpoint is the difference in the Combined Assessment of Function and Survival (CAFS) ranked score at 52 weeks after treatment initiation. Additional, secondary functional efficacy (ALSFRS-R, percent SVC, muscle strength, quality of life, and caregiver burden) and safety endpoints will be analyzed at 52 weeks. After the placebo-controlled period, all patients will have the option to receive pegcetacoplan in an open-label period for an additional 52 weeks. Results: This ongoing study is currently enrolling participants. Conclusions: Results of this study will determine the role of complement and C3 inhibition in patients with ALS.