Interest in the phase-changing material vanadium dioxide as a potential reconfigurable or modulating element in optical and electronic applications has been a major driver for research since the material was first characterized half a century ago. The thermally induced phase transition occurs near 70˚C, and comprises an insulator-to-metal transition with a four-orders-of-magnitude increase in free-carrier density, and a nearly, but not quite, simultaneous structural phase transition from the monoclinic ground state to the rutile (tetragonal) excited state. Although early switching experiments focused on the thermally driven phase transition, a laser-driven phase transition in vanadium dioxide was observed already in 1965. However, a detailed understanding of the mechanisms underlying the photo-induced phase transition (PIPT) remained elusive, especially for the ultrafast PIPT, first demonstrated two decades ago. This review discusses the current understanding of the PIPT as revealed both in recent experiments and theory for both VO2 thin films and single crystals during the past decade. Specific issues to be considered include the partitioning of laser-imparted energy into electronic and phononic degrees of freedom during the PIPT; band-gap collapse and the dynamical evolution of the rutile structural phase; effects of coupling between thin film and substrate; variations in PIPT dynamics with laser wavelength and material optical properties; and ultimate limitations on the switching speed and energy cost for the transition. This detailed mechanistic understanding has specific implications for applications of the PIPT in silicon photonics, which will be discussed in conclusion.