The major types of AIGaAs high-power cw single-mode diode lasers are reviewed and compared. The basic approaches for achieving high-power (20 to 50 mW/facet) single-mode operation are presented first. Emphasis is placed on the CDH-LOC (constricted double-heterojunction large optical cavity) laser type, which has demonstrated cw single-mode operation to 40 mW/facet and 50% duty cycle fundamen-tal mode operation to 100 mW/facet. By using CDH-LOC devices, signal-to-noise ratios close to 70 dB were achieved, and peak powers of 40 mW (50% duty cycle) were coupled into 0.2 N.A. fibers. Life tests of CDH-LOC lasers at 40 mW/facet initial output power and 50% duty cycle have shown small drops in output even after 10,000 hours of operation. Monolithic ten-unit arrays of CDH-LOC lasers delivering up to 300 mW in cw operation have been demonstrated as well.