Understanding poststroke upper limb impairment is essential to planning therapeutic efforts to restore function. However, determining which upper limb impairment to treat and how is complex because the impairments are not static and multiple impairments may be present simultaneously. How impairments contribute to upper limb dysfunction may be understood by examining them from the perspective of their functional consequences. There are 3 main functional consequences of impairments on upper limb function: (1) learned nonuse, (2) learned bad use, and (3) forgetting as determined by behavioral analysis of tasks. The impairments that contribute to each of these functional limitations are described.