Massive MIMO is a promising technology for next-generation wireless systems, offering significant improvements in energy efficiency, spectral efficiency, and robustness. It involves using a large number of antennas at the base station to serve multiple terminals simultaneously, enabling spatial multiplexing and efficient resource allocation. Unlike traditional multi-user MIMO, which uses a similar number of antennas and terminals, Massive MIMO uses a large excess of service-antennas over terminals and operates in time-division duplex mode. This allows for focused energy transmission, reducing interference and improving throughput. Massive MIMO also benefits from the use of inexpensive, low-power components, reduced latency, and simplified media access control. However, it presents new challenges, such as managing pilot contamination, ensuring synchronization, and optimizing hardware for low-cost, low-precision components. The technology relies on the law of large numbers to average out noise, fading, and hardware imperfections, making it resilient to interference. Massive MIMO has the potential to significantly increase capacity and energy efficiency, with simulations showing that it can achieve up to 10 times higher capacity and 100 times greater energy efficiency. Despite its advantages, challenges remain, including channel reciprocity, pilot contamination, and hardware impairments. Research is ongoing to address these issues and to develop practical implementations of Massive MIMO, including testbeds and prototypes. The technology is expected to play a key role in future wireless networks, enabling high-speed, energy-efficient communication and supporting new deployment scenarios.Massive MIMO is a promising technology for next-generation wireless systems, offering significant improvements in energy efficiency, spectral efficiency, and robustness. It involves using a large number of antennas at the base station to serve multiple terminals simultaneously, enabling spatial multiplexing and efficient resource allocation. Unlike traditional multi-user MIMO, which uses a similar number of antennas and terminals, Massive MIMO uses a large excess of service-antennas over terminals and operates in time-division duplex mode. This allows for focused energy transmission, reducing interference and improving throughput. Massive MIMO also benefits from the use of inexpensive, low-power components, reduced latency, and simplified media access control. However, it presents new challenges, such as managing pilot contamination, ensuring synchronization, and optimizing hardware for low-cost, low-precision components. The technology relies on the law of large numbers to average out noise, fading, and hardware imperfections, making it resilient to interference. Massive MIMO has the potential to significantly increase capacity and energy efficiency, with simulations showing that it can achieve up to 10 times higher capacity and 100 times greater energy efficiency. Despite its advantages, challenges remain, including channel reciprocity, pilot contamination, and hardware impairments. Research is ongoing to address these issues and to develop practical implementations of Massive MIMO, including testbeds and prototypes. The technology is expected to play a key role in future wireless networks, enabling high-speed, energy-efficient communication and supporting new deployment scenarios.