This review discusses the mechanics and statistics of active matter, focusing on systems of self-propelled particles. Active matter includes living organisms and their motile components, such as molecular motors. The article presents a unified view of active matter, covering both living and inanimate systems. It discusses the collective behavior of active matter using principles from nonequilibrium statistical mechanics and hydrodynamics. The review highlights the unique mechanical properties of active matter, such as long-range order and giant number fluctuations, and their implications for macroscopic rheology. It also explores the physics of flocks, the cytoskeleton as an active gel, and the behavior of swimming organisms. The review discusses the theoretical framework for active hydrodynamics, including the Toner-Tu field theory, and its applications to various systems. It also addresses the effects of activity on viscosity and the instability of active suspensions. The review concludes with a discussion of experiments on active suspensions, including viscosity measurements and the structure factor of fish shoals. The article emphasizes the importance of understanding active matter for controlling and mimicking active cellular systems.This review discusses the mechanics and statistics of active matter, focusing on systems of self-propelled particles. Active matter includes living organisms and their motile components, such as molecular motors. The article presents a unified view of active matter, covering both living and inanimate systems. It discusses the collective behavior of active matter using principles from nonequilibrium statistical mechanics and hydrodynamics. The review highlights the unique mechanical properties of active matter, such as long-range order and giant number fluctuations, and their implications for macroscopic rheology. It also explores the physics of flocks, the cytoskeleton as an active gel, and the behavior of swimming organisms. The review discusses the theoretical framework for active hydrodynamics, including the Toner-Tu field theory, and its applications to various systems. It also addresses the effects of activity on viscosity and the instability of active suspensions. The review concludes with a discussion of experiments on active suspensions, including viscosity measurements and the structure factor of fish shoals. The article emphasizes the importance of understanding active matter for controlling and mimicking active cellular systems.