The main advantages of vertical cavity surface emitting lasers (VCSELs) are low threshold current, a circular output-beam profile, high modulation bandwidth, single-longitudinal-mode operation and easy two-dimensional integration with high density. A single transverse mode VCSEL is considered to be a desired light source for optical communication, high-speed local-area networks, and optical interconnect. After analysing structural and modal features of a VCSEL, important progress of single transverse mode VCSELs is presented and discussed. Finally, prospect and problems of future research are presented.