Adverse outcome pathway (AOP) was a conceptual construct that integrated existing knowledge concerning the pathway of causal linkages between a molecular initiating event (MIE) and a final adverse effect at individual or population levels. The AOP methodology could be used as a basis for effects extrapolation and was an approach towards providing a framework for collecting and evaluating relevant chemical, biological and toxicological information. The framework would play an important role in risk assessment. We reviewed the concept of AOP, the development and assessment of the framework and the established models in toxicology researches. And the prospects and challenges of its application in toxicology were also introduced.