This paper reports the recent progress on the development of GaSb-based vertical-cavity surface-emitting lasers (VCSELs) with a record-long emission wavelength of above 4 μm using type-II quantum wells. Mid-wave infrared (MWIR) spectral region, covering the 3-6 μm wavelength range, is technologically very interesting for enabling two major application areas such as sensing and defense/security. Among several types of diode lasers, electricallypumped continuous-wave operating VCSELs seem to be the most attractive choice owing to their low-power consumption, inherent longitudinal single-mode emission, and simple electro-thermal wavelength tunability. The applicability of MWIR VCSELs for these two major areas are also discussed in this paper. Single-mode low-power (a few mWs) VCSEL operating at room-temperature with reasonable tunability is essential for the sensing application. For the advanced military application, high optical power (with at least a few watts), high-efficiency and high-brightness (>1 W/mm<sup>2</sup>) MWIR lasers are important. Given that the MWIR wavelength regime is eye-safe and has a low-loss atmospheric window, the development of next-generation MWIR laser sources is currently in high demand.