This volume highlights recent work by researchers in Western and Central Africa on nonlinear analysis, geometry, and state-of-the-art applications. The papers are based on presentations from the fourth "Nonlinear Analysis, Geometry, and Applications Biennial International Research Symposium," held December 1-6, 2025 at University Gaston Berger of Saint Louis, Senegal. Organized around mathematical modeling, analysis, and geometry, the contributions address timely applications such as coastal erosion, urban networks, pollution, and population dynamics. Nonlinear Analysis, Geometry, and Applications will be of use to students and researchers interested in exploring recent advances in these active research areas.