This thesis examined changes in the definition and concept of internal control over the period in which the definition published by the American Institute of Accountants in 1949 was in effect. Evolution of internal control took place under the influence of conflicting pressures: the desire of auditors to reduce their liability, and therefore to define their responsibilities narrowly; and a trend, influenced by a number of factors, towards evaluating the broad concept of control over an organization as a whole. Examining the evolution of internal control over this period provided an indication of the nature of change in auditing, and the pressures which induce change.