Modulation techniques may be classified as either single-carrier that employ a single RF carrier or multicarrier where information is transmitted in parallel by using multiple RF subcarriers. Orthogonal frequency division multiplexing (OFDM) is a well-known multicarrier modulation technique. The great advantage of OFDM and other multicarrier schemes is their ease of implementation with common DSP processing functions such as the Fast Fourier Transform (FFT) and its inverse (IFFT). Moreover, for channels with ISI, equalization can be done efficiently in the frequency domain instead of more complicated time-domain equalization. Finally, the maximum likelihood receiver is straightforward to implement in digital baseband with simple processing. This chapter begins with the basic description of OFDM signals. It is shown that the OFDM baseband modulator and demodulator can be efficiently implemented by using an inverse discrete-time Fourier transform (IDFT) and discrete Fourier transform (DFT), respectively. Next, the error probability performance of OFDM is considered for flat fading channels with AWGN. The chapter concludes with simple frequency-domain equalization and detection for OFDM on channels with ISI and AWGN.