Textbook in PDF format Mathematics in the twenty-first century is no longer confined to isolated theories or purely abstract constructions. It has become a unifying language for complexity, uncertainty, computation, and decision-making across science, technology, and society. From artificial intelligence and data-driven models to networks, collective behavior, and nonlinear dynamics, modern mathematics operates at the intersection of theory, computation, and real-world systems. The collection is designed to reflect this transformation. Rather than presenting mathematics as a static body of results, the series emphasizes conceptual foundations, modeling tools, and dynamical thinking—the mathematical ideas that underpin contemporary scientific and technological advances. This work is organized as a coherent progression of volumes, each addressing a core pillar of modern applied and theoretical mathematics. Together, they form a roadmap that connects classical mathematical roots to emerging paradigms such as machine learning, agent-based modeling, and complex systems. Volume 0 — Roots of Mathematics The series begins by revisiting the historical and conceptual foundations of mathematics. Volume I — Mathematical Foundation Tools This Volume provides the essential toolkit required throughout the series. Topics include probability, statistics, linear algebra, calculus and basic discrete mathematics. Volume II — Optimization Optimization lies at the heart of modern science and engineering. This Volume introduces optimization as both a mathematical discipline and a modeling framework, covering unconstrained and constrained optimization, convexity, gradient-based methods, stochastic approaches and game theory. Volume III — Networks Complex systems are often best understood through their relational structure. Volume III develops the mathematics of networks and graphs, including connectivity, centrality, flows, diffusion processes, and network dynamics. Volume IV — Agent-Based Models Moving beyond aggregate equations, this Volume focuses on microscopic rules and emergent behavior. Agent-based modeling provides a powerful framework for studying collective phenomena arising from individual interactions. Volume V — Dynamics and Fractals This Volume addresses systems that evolve over time, often in nonlinear and unpredictable ways. It introduces dynamical systems, stability, bifurcations, chaos, and fractal geometry. Volume VI — Machine Learning and Artificial Intelligence The final Volume connects mathematics directly to intelligent systems. It presents the mathematical foundations of machine learning and artificial intelligence, including classical models, neural networks, and transformers. A Unified Vision Across all Volumes, Math for the XXI Century promotes a unified vision of mathematics as: a language for modeling complex systems, a bridge between theory and computation, and a foundation for intelligent, adaptive technologies. The collection is intended for students, researchers, and practitioners who seek not only mathematical techniques, but a conceptual framework for understanding and shaping the complex world of the twenty first century