Selection of chemical marker is critical to the quality control and standardization of medicinal herbs. The ideal chemical marker is the active principle with demonstrated clinical efficacy contributing to the therapeutic effect of the herb, while the worst ones are the analytical marker and “phantom” marker whose pharmacological actions are unknown, uncontrollable or unpredictable. In this article, we explore the seven categories of chemical markers, discuss the pitfalls of choosing them, and illustrate the problems using a traditional Chinese medicinal herb Ligusticum chuanxiong as an example.