Orthogonal frequency-division multiplexing (OFDM) has existed for many years, but it has recently acquired a huge momentum as an emerging technology for high data rates. This technology has quickly moved from books and lectures to be a key technique within almost all wireless commercial broadband technologies. OFDM stands as a low complexity and high efficiency way to deal with the channel frequency selectivity by dividing the channel into a large set of sub-channels, each one of them showing flat fading characteristics. Therefore, OFDM is a multi-carrier transmission technique that makes the communication to be robust against large delay spreads by keeping the orthogonality in the frequency domain. This book presents current research on the advantages and disadvantages of OFDM.