In this article, expertise in simultaneous interpreting is defined as the result of well-practiced strategies in each of the comprehension, translation, and production processes, and the interaction among these processes, which are specific to the needs of the task of simultaneous interpreting. What allows the interaction among the comprehension, translation, and production processes to act in sync is interpreters’ ability to manage their mental resources in an efficient manner, particularly in the way attention is managed. Expert-novice difference is examined by comparing skills and sub-skills, by analyzing the cognitive abilities underlying the act of simultaneous interpreting, and by providing evidence and counter-evidence from Interpreting Studies and cognitive science.