Multiple input multiple output (MIMO) systems have been used for many years in the field of wireless communications. The huge increase in coverage and capacity offered by MIMO technology are the key benefits of using multiple sensors at the transmitter and receiver . Recently, MIMO technology has been applied in the context of power line communications (PLCs), with the aim of offering higher channel capacity and therefore larger system coverage, by including the use of the protective earth (PE) wire in addition to the line (L) and neutral (N) wires. SNR values observed in typical PLC scenarios can be much higher than in the case of a classical wireless communication. This high SNR condition is beneficial for MIMO transmission, as it ensures a high capacity gain with respect to single input single output (SISO) transmission, even if the channel presents a high degree of spatial correlation. This chapter is divided into two main sections. First, the PLC channel capacity offered by MIMO technology is analysed in details. The channel capacity provides an upper limit for achievable throughput and does not take system implementation or a particular MIMO scheme into consideration. The achievable throughput for different MIMO schemes in an OFDM system with adaptive modulation is then investigated.