In the high water cut development stage of oilfields, selective water shutoff technology is crucial for enhancing oil recovery. Emulsion-based water shutoff technology has emerged as a research and application hotspot due to its advantage of selective plugging. This paper systematically reviews the mechanisms of selective water shutoff using emulsions, including core processes such as viscosity increase and mobility control, physical plugging and Jamin effect, and rock wettability alteration. The influences of various factors on emulsion stability, such as emulsifier type, pH value, temperature, salinity, and crude oil composition, are analyzed in detail. Traditional emulsion-based water shutoff systems (active heavy oil-based and emulsion-based) and their stabilization technologies are summarized and compared. Furthermore, novel heavy oil emulsion phase inversion water shutoff systems are introduced, and the phase inversion mechanisms and technical progress based on salinity and pH control are discussed.