This paper investigates the performance and optimization of movable antenna (MA)-aided wideband communications using orthogonal frequency division multiplexing (OFDM) in frequency-selective fading channels. The authors derive an upper bound on the achievable OFDM rate in the high-SNR regime when the size of the Tx/Rx region for antenna movement is arbitrarily large. They also develop a parallel greedy ascent (PGA) algorithm to optimize the MA positions for maximizing the OFDM rate under finite-size Tx/Rx regions. A simplified PGA algorithm is proposed to reduce computational complexity. Simulation results show that the proposed PGA algorithms can approach the OFDM rate upper bound closely with increasing Tx/Rx region sizes and outperform conventional systems with fixed-position antennas (FPAs) under wideband channel conditions.This paper investigates the performance and optimization of movable antenna (MA)-aided wideband communications using orthogonal frequency division multiplexing (OFDM) in frequency-selective fading channels. The authors derive an upper bound on the achievable OFDM rate in the high-SNR regime when the size of the Tx/Rx region for antenna movement is arbitrarily large. They also develop a parallel greedy ascent (PGA) algorithm to optimize the MA positions for maximizing the OFDM rate under finite-size Tx/Rx regions. A simplified PGA algorithm is proposed to reduce computational complexity. Simulation results show that the proposed PGA algorithms can approach the OFDM rate upper bound closely with increasing Tx/Rx region sizes and outperform conventional systems with fixed-position antennas (FPAs) under wideband channel conditions.