The article provides an overview of modular self-reconfigurable robots, highlighting their architecture, motivations, applications, and future challenges. Modular robots are composed of multiple building blocks with uniform docking interfaces, allowing for the transfer of mechanical forces, electrical power, and communication. These systems can be classified into lattice, chain/tree, and mobile architectures, each with distinct advantages and control strategies. The key motivations for designing these systems include versatility, robustness, and low cost. Applications such as space exploration and long-term consumer robotics showcase the potential of modular self-reconfigurable systems. Despite significant progress, challenges remain in hardware design, planning and control algorithms, and application domains. Future grand challenges include scaling up to larger systems, achieving self-repair, self-sustaining operations, self-replication, and reconciling with thermodynamics. The article concludes by emphasizing the potential of modular self-reconfigurable systems to revolutionize robotics and automation.The article provides an overview of modular self-reconfigurable robots, highlighting their architecture, motivations, applications, and future challenges. Modular robots are composed of multiple building blocks with uniform docking interfaces, allowing for the transfer of mechanical forces, electrical power, and communication. These systems can be classified into lattice, chain/tree, and mobile architectures, each with distinct advantages and control strategies. The key motivations for designing these systems include versatility, robustness, and low cost. Applications such as space exploration and long-term consumer robotics showcase the potential of modular self-reconfigurable systems. Despite significant progress, challenges remain in hardware design, planning and control algorithms, and application domains. Future grand challenges include scaling up to larger systems, achieving self-repair, self-sustaining operations, self-replication, and reconciling with thermodynamics. The article concludes by emphasizing the potential of modular self-reconfigurable systems to revolutionize robotics and automation.