Multiple-Input Multiple-Output technology revolutionizes wireless performance by using multiple antennas at both the transmitter and receiver to send several independent data streams simultaneously over the same frequency channel. Rather than requiring additional spectrum, MIMO exploits the spatial dimension of the radio environment where signals traveling along different physical paths between antenna pairs create separable communication channels. A 2x2 MIMO system can theoretically double throughput, 4x4 MIMO can quadruple it, and the massive MIMO configurations used in 5G with 64 transmit and 64 receive elements unlock unprecedented spectral efficiency and multi-user capacity.