Today, many wired and wireless communication systems use orthogonal frequency division multiplexing (OFDM) technology. The use of OFDM in optical systems is attracting increasing interest. However, one of the major drawbacks of OFDM for very high data rate applications is its sensitivity to timing errors such as timing jitter. The original work presented in this thesis is a study of the timing jitter problem in high speed OFDM systems including wireless and optical systems.