She helped found MoMA and pioneered the promotion of work of American and French modern artists at the turn of the 20th century, but until now, her life and legacy remain woefully under examined. An early pioneer and patron of French and American modernism, Lillie P. Bliss (1864-1931) was one of three female cofounders of MoMA in 1929, and went on to furnish the museum with one of the finest collections of modern art in the world. Presenting case-studies alongside data-driven analysis drawn from original research into the American art market, this book reconstructs Bliss's influential career in rich and compelling detail. It weaves together extensive archival material related to the art and the artists that Bliss collected and patronised - such as Paul Cezanne, Pierre-Auguste Renoir, Edgar Degas, Georges Seurat, and Odilon Redon - the art market of the time and the evolution of the New York museum ecosystem, and highlights the importance of private collecting in the development of American museums. By revisiting MoMA's foundational history, author Irene Walsh explores how Lillie P. Bliss's visionary bequest of over 120 artworks upon her death in 1931 profoundly influenced and shaped the institution, questioning why her pioneering role has been overshadowed by other collectors. Combining biography, market knowledge, institutional analysis, and art history, it enriches our understanding of early 20th-century dealer dynamics and collection strategies in New York, illuminates the role of collections in shaping art narratives, while offering contemporary insights into women's agency in the arts. Global, interdisciplinary, and timely, the book provides fascinating first-hand research into a collector of great importance, and will make a long standing contribution to studies in the art market and 20th-century collecting.