BACKGROUND AND PURPOSE-: Constraint-induced movement therapy is a set of treatments for rehabilitating motor function after central nervous system damage. We assessed the roles of its 2 main components. METHODS-: A 2×2 factorial components analysis with random assignment was conducted. The 2 factors were type of training and presence/absence of a set of techniques to facilitate transfer of therapeutic gains from the laboratory to the life situation (Transfer Package; TP). Participants (N=40) were outpatients ≥1-year after stroke with hemiparesis. The different treatments, which in each case targeted the more affected arm, lasted 3.5 hours/d for 10 weekdays. Spontaneous use of the more affected arm in daily life and maximum motor capacity of that arm in the laboratory were assessed with the Motor Activity Log and the Wolf Motor Function Test, respectively. RESULTS-: Use of the TP, regardless of the type of training received, resulted in Motor Activity Log gains that were 2.4 times as large as the gains in its absence (P<0.01). These clinical results parallel previously reported effects of the TP on neuroplastic change. Both the TP and training by shaping enhanced gains on the Wolf Motor Function Test (P<0.05). The Motor Activity Log gains were retained without loss 1 year after treatment. An additional substudy (N=10) showed that a single component of the TP, weekly telephone contact with participants for 1 month after treatment, doubled Motor Activity Log scores at 6-month follow-up. CONCLUSIONS-: The TP is a method for enhancing both spontaneous use of a more affected arm after chronic stroke and its maximum motor capacity. Shaping enhances the latter. © 2013 American Heart Association, Inc.