Priming effect is a strong, short-term change in the turnover of soil organic carbon (SOC) caused by exogenous substrates. Addition of exogenous substrates may accelerate SOC decomposition-a positive priming effect, and also may retard SOC decomposition-a negative priming effect. Priming effects are governed by many factors, such as quantity and quality of the exogenous substrates and the soil properties. In this paper a review is presented to elucidate direct driving factors, mechanisms and quantification of the priming effect by compiling papers using isotope techniques (¹³C and ¹⁴C), and to put forward items to be further studied.