Semiconductor disk lasers (SDLs), also known as optically pumped vertical external-cavity surface-emitting lasers (VECSELs), offer unparalleled features combining high beam quality, large wavelength coverage, multi-watt output power, narrow linewidth, and broad tuning range. Moreover, relative to the features they provide, SDLs are compact and cost-effective systems. Their unique properties have already been recognized in biophotonics, for example, in photocoagulation treatment of macular degeneration using yellow radiation and multiphoton imaging, yet their full spread to applications is still to come. This chapter provides an overview of key technology concepts related to SDLs and a summary of the most important developments in terms of wavelength coverage and output powers. Specific developments are presented for SDLs emitting continuous wave (CW) radiation at the yellow-orange-red optical spectrum and for SDLs emitting picosecond pulses at red wavelengths. The chapter is concluded with a review of several biophotonics applications and their needs for laser sources, which are then put in a perspective of current SDL achievements.