Patients with platinum-resistant or -refractory high-grade serous ovarian cancer (HGSOC) have a poor prognosis, and their management represents a substantial unmet medical need. Preclinical data and results from a phase Ib trial demonstrated the efficacy and tolerability of the combination of the α-specific phosphatidylinositol-3-kinase (PI3K) inhibitor alpelisib plus the poly(adenosine diphosphate-ribose) polymerase (PARP) inhibitor olaparib in platinum-resistant, non- BRCA-mutated ovarian cancer. Here, we describe the study design and rationale for the phase III, multicenter, open-label, randomized, active-controlled EPIK-O/ENGOT-OV61 trial investigating alpelisib in combination with olaparib compared with standard-of-care chemotherapy in patients with platinum-resistant or -refractory HGSOC with no germline BRCA mutation. Progression-free survival (blinded independent review committee) is the primary end point. Overall survival is a key secondary end point. Clinical Trial Registration:: NCT04729387 ( ClinicalTrials.gov )