Manipulation and characterization of information using ultrafast optical signals is critical for numerous applications in telecommunications, biology, quantum information science, spectroscopy, and atomic and molecular physics. Femtosecond pulsed laser sources are available over a wide range of wavelengths and repetition rates, which enable the generation, transmission, and characterization of information at bandwidths beyond 1 THz. In this article, we review the concept of space–time duality as a system design tool for ultrafast optical processing and characterization. The combination of this design framework with recent advances in nonlinear optical devices enables the realization of highly complex signal processing systems that can generate, characterize, and manipulate arbitrary and non-repetitive optical waveforms at unprecedented processing speeds.