<p>Purkinje cells (PCs) mediate adaptive cerebellar output through inhibitory control of the cerebellar nuclei. Because many PCs converge, their influence on target neurons likely depends on population activity. However, despite a large literature on individual PC relationships with behavior, little is known about how multiple PCs collaborate to influence movement. In simultaneously recorded PCs during mouse forelimb reach behavior, we found that different kinematic variables correlated either with PC firing rates or covariance: reach velocity and deceleration correlated with firing rates, while the coordination of these kinematic variables, which influences reach amplitudes, was related to covariance. In a model, physiological levels of PC covariance elevated nuclear firing rates, which could promote faster reach deceleration than the same conditions with low covariance. These findings suggest a role for coherent PC population activity to coordinate movement.</p>