Since its design in 2003, the joint Simon task and corollary joint Simon effect (JSE) have been invaluable tools towards the study of joint action and the understanding of how individuals represent the action/task of a co-actor. The purpose of this meta-analysis was to systematically and quantitatively review the sizeable behavioural evidence for the JSE. Google Scholar was used to identify studies citing the first report of the joint Simon task (Sebanz, Knoblich, & Prinz, 2003) up until June 23, 2015. After screening, thirty-nine manuscripts were included in the meta-analysis, thirteen of which included individual go/no-go (IGNG) control data. Separate random-effects models were conducted for both the joint Simon and IGNG datasets, and meta-regression models were used to assess potential moderators that may impact the strength of the JSE. The results provide an important quantitative summary of the literature and serve as a foundation for future research surrounding the JSE.