Trills by skilled pianists were studied by using a piano in which the on-off timing and dynamic level (hammer velocity) of notes were recorded digitally. In addition, finger flexion-extension accelerations and elecromyographic (EMG) activity were monitored simultaneously and digitized. The data allow estimates to be made of joint angle, duration of contact between finger and key, and time from finger-key contact to note onset. Finger accelerations and EMG activity appear at characteristic phases of the trill cycle; their magnitude and timing depend on trill speed, dynamic level, and the locus at which the finger strikes the key. The data document the considerable speed and precision with which skilled performers can execute trills.