Experimental psychologists have traditionally been suspicious of the uncon scious. However, as is clear from other chapters in this volume, there is now widespread experimental support for the claim that in the domains of perception and memory important cognitive processes occur outside the realm of conscious awareness. But what of problem solving? Perhaps more than any other area of cognitive psychology, problem solving abounds in anecdotes of unconscious processes. Solutions are reached with sudden flashes of insight or leaps of intuition that defy introspective causal analysis. Such alleged implicit processes are among the most persistently reported but least understood phenomena in cognitive psychology.