We discuss the advantages of wavelength-division-multiplexed (WDM) lightwave systems and the need for monolithically integrated multiwavelength laser arrays. For WDM light-wave systems to be cost effective, it is important to reduce the per-wavelength component cost. By photonic integration, the packaging and the control circuitry will be shared among all the wavelengths. In this paper, we review the multiwavelength laser arrays, the array coupling, and the photonic integration approach. We have demonstrated the monolithic integration of a 21-wavelength multi-quantum-well distributed-feedback laser array with a star coupler and optical amplifiers on the same chip. Operating a packaged module under CW operation, we obtained as many as 15 individual wavelengths simultaneously launched from one output port of the star coupler of this integrated chip into one lensed single-mode fiber. We also characterized the thermal and the electrical crosstalk from the neighboring lasers. This integrated chip stands a good chance of being a compact and low-cost multiwavelength laser source for future WDM lightwave systems.