Many common behaviours such as moving a table, rowing a boat, and producing music require individual performers to coordinate their actions. Researchers have only begun to investigate the mechanisms of perception, action, and cognition that support these types of joint action (Galantucci and Sebanz, 2009). It has recently been suggested that the activation of mental representations of others’ actions may underlie successful joint action (Sebanz and Knoblich, 2009). However, it has also been argued that temporal coordination may be explained by dynamical principles that govern coordination between oscillating systems, without relying on higher-level cognitive representations (Marsh, Richardson, and Schmidt, 2009). The proposed research employs experimental analogs of ensemble music performance, in which two or more people produce separate musical sequences whose pitches are temporally coordinated, to determine a) whether representations of a co-performer’s actions are activated in temporally coordinated joint action and b) which components of the actions are represented by co-performers. The first question is addressed by comparing both behaviour and functional brain activity when people perform sequences alone and with another person. The second question is addressed by measuring neural activity in response to incongruence between the movements and pitches produced by co-performers and in response to violations of expectation about a co-performer’s pitch and timing. The proposed research will unite the applicant’s expertise in studying coordinated action using musical tasks with the European host's expertise in representation-based accounts of joint action. In doing so, the research will bridge the gap between two theoretical approaches to action coordination, and will further understanding of the mechanisms by which people produce the complex coordination they so easily achieve in everyday life.