Does interference, a primary source of forgetting in explicit memory, also affect implicit memory? Several early and highly influential studies have suggested that implicit memory is immune to interference. In contrast, a number of subsequent investigations have reported evidence for interference. As well, amnesic patients, whose performance relies primarily on implicit memory, often show interference effects. A review of methods, materials, and findings suggests that interference occurs on implicit tests when targets and nontargets are similar and so compete as potential responses to the memory cue. Further, there is some evidence that the degree of interference on implicit tasks is affected by the number of competing items and their strength relative to the target. Interference effects in implicit memory seem to parallel those in explicit memory, and the authors consider the implications of this conclusion for theoretical concepts of memory and the brain.