The 11 invited and 37 contributed papers in this special issue focus on nonlinear-optical signal processing. Topics covered include: nonlinear pulse shaping; 2R and 3R regeneration; all-optical clock recovery; optical limiting; optical bistability; all-optical switching/gating; optical data format conversion; wavelength conversion; phase conjugation; phase-sensitive amplification; optical delay lines; optical burst/packet switching; all-optical OTDM multiplexing/demultiplexing; and micro- and nano-scale nonlinear-optical devices.