MIMO has become an essential element of wireless communication standards including IEEE 802.11n.
For around a hundred years, single antennas have been used, dipoles, etc. for wireless communications.
In the last ten years, however, this has all changed and multiple antenna systems(Massive MIMO), different types of diversity, beamforming, array antennas and MIMO have all emerged onto the wireless scene.
They offer better cell capacity, more user throughput, larger cells: too many good things to be true, it seems. However, actual deployments have shown the immense value of current MIMO technology and the potential for the next few years.