As the demand for network bandwidth is growing explosively, the deployment of the wavelength division multiplexing technology is extending from the backbone network to the metropolitan area network and the access networks. Low-cost tunable semiconductor lasers, which are the core components of wavelength division networks, are attracting increasing attention. This paper reviews the development of semiconductor tunable lasers, describes the working principles and performance of various tunable lasers, and analyzes the advantages and disadvantages of typical commercial tunable optical modules. The research and industrial application progress of low-cost tunable V-cavity lasers are mainly introduced.