Nisbett & Wilson (1977a) proposed that people lack ‘introspective access' to their mental processes, and that retrospective causal reports about those processes are in general inaccurate. This paper reviews the literature subsequent to that proposal. This literature has established that: (i) the term ‘process' lacks clear, adequate and valid definition; (ii) the proposal depends upon an untested assumption that verbal reports are valid indicators of ‘introspective access’; (iii) knowledge of the process is not sufficient for an accurate report about causal relations between stimuli and responses. Hypotheses about causal report accuracy can be tested, but there are severe methodological difficulties associated with measures of actual effects, the conditions under which retrospective causal reports are given and the use of ‘observer’ groups to rule out specific sources of information. Of the recent studies, none has achieved unambiguous support for, or falsification of, even a weak form of the proposal. There is no justification at present for using the proposal to interpret null results on verbal report measures. Some issues of broader significance are discussed, including the usefulness of verbal reports in research, the place of cultural beliefs in theoretical statements, and the social and practical context of verbal reports.