With ever increasing power dissipation in electronic chips that are shrinking in size, cooling demands are becoming more severe. Forced air cooling is reaching its operational limits, and single-phase liquid cooling in microchannels has been able to accommodate the rising heat fluxes. Further increases in computing (chip) power suggest that a switch from single-phase to boiling heat transfer will be needed. A major impediment to using boiling or forced convective vaporization for such a cooling application is the limiting critical heat flux (CHF) condition. In this paper, the CHF condition in microchannels is reviewed. Data from the literature are discussed, and new data for a range of operating and geometric conditions are presented. Influencing factors, parametric trends, phenomenological models, and other aspects of the CHF condition are discussed.