The physics of microswimmers, both biological and synthetic, is a key area of study in understanding locomotion and collective behavior at the microscale. Microorganisms, such as bacteria, sperm, and algae, use flagella for propulsion, while synthetic microswimmers employ chemical or thermal energy to move. At low Reynolds numbers, where viscous forces dominate, traditional macroscopic propulsion mechanisms are ineffective. Microorganisms have evolved strategies to overcome and exploit drag, such as rotating helical flagella or whip-like flagella in eukaryotic cells. Synthetic microswimmers, on the other hand, may use alternative methods to convert energy into directed motion, potentially more efficient than biological ones. The dynamics of microswimmers involve various propulsion mechanisms, including the synchronized beating of flagella and cilia, and their behavior near surfaces. Collective behavior, such as swarming and cooperation, is also significant, with microswimmers exhibiting complex patterns like networks and vortices. The study of microswimmers includes both biological and synthetic systems, with a focus on their hydrodynamics, synchronization, and interactions. Theoretical models, such as the Purcell swimmer and squirmers, help elucidate the physical principles underlying microswimmer motion. These models are essential for understanding how microswimmers navigate and interact in their environments, with applications in medicine, biology, and materials science. The review highlights the importance of hydrodynamic interactions, the role of flagellar motion, and the challenges in designing efficient and controllable microswimmers.The physics of microswimmers, both biological and synthetic, is a key area of study in understanding locomotion and collective behavior at the microscale. Microorganisms, such as bacteria, sperm, and algae, use flagella for propulsion, while synthetic microswimmers employ chemical or thermal energy to move. At low Reynolds numbers, where viscous forces dominate, traditional macroscopic propulsion mechanisms are ineffective. Microorganisms have evolved strategies to overcome and exploit drag, such as rotating helical flagella or whip-like flagella in eukaryotic cells. Synthetic microswimmers, on the other hand, may use alternative methods to convert energy into directed motion, potentially more efficient than biological ones. The dynamics of microswimmers involve various propulsion mechanisms, including the synchronized beating of flagella and cilia, and their behavior near surfaces. Collective behavior, such as swarming and cooperation, is also significant, with microswimmers exhibiting complex patterns like networks and vortices. The study of microswimmers includes both biological and synthetic systems, with a focus on their hydrodynamics, synchronization, and interactions. Theoretical models, such as the Purcell swimmer and squirmers, help elucidate the physical principles underlying microswimmer motion. These models are essential for understanding how microswimmers navigate and interact in their environments, with applications in medicine, biology, and materials science. The review highlights the importance of hydrodynamic interactions, the role of flagellar motion, and the challenges in designing efficient and controllable microswimmers.