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.

Diaraf Seck is full Professor in Mathematics, PI and lead researcher in NLAGA network. His topics of interest are: Geometrical Analysis of Optimal Shapes, Calculus of Variations, PDE, Homogenization, Optimal Transport and Mathematical Modeling.

Kinvi Kangni is full Professor in Mathematics and lead researcher in NLAGA network. His topics of interest are: Harmonic and Functional Analysis.

Philibert Nang is full Professor in Mathematics and lead researcher in NLAGA network. His topics of interest are: Algebraic Analysis and Algebra. Recipient of the ICTP Ramanujan Prize 2011.

Marie Salomon Sambou is full Professor in Mathematics and lead researcher in NLAGA network . His topics of interest are: Complex Geometry and Complex Analysis of several variables.

Mouhamed Moustapha Fall is full Professor in Mathematics. His topics of interest are: Geometry and Geometric PDE, Regularity of PDE. Recipient of the ICTP Ramanujan Prize 2022.