Over the past four decades, mathematical problem posing has represented a growing field within mathematics education, recognized for its potential to foster creativity, conceptual understanding, and student agency. This new volume presents an integrated, state-of-the-art synthesis of theoretical, empirical, and pedagogical advances in mathematical problem posing. The book traces the historical roots and evolving significance of problem posing, explores the cognitive and affective dimensions of problem-posing processes, introduces empirical models and frameworks for analyzing posing behaviors, and demonstrates how these processes vary across contexts. Chapters also address how students and teachers engage with problem posing across developmental stages, curricular settings, and cultural contexts. The volume highlights problem posing as a means of authentic assessment and instructional differentiation. Finally, the book discusses future research directions aimed at broadening access, deepening understanding, and embedding problem posing as a core pedagogical approach across educational systems.