The preparation of school timetables is a task which requires ‘human’ decisions to be made yet which is tedious and time-consuming when carried out by hand. This thesis presents a new interactive timetabling system which shares the task between man and machine according to the respective abilities of each. The system was designed with two objectives in mind. The first was to enable the timetabler to observe the state of the timetable and to manipulate lessons as easily as he could in the manual method. This was achieved by the provision of computer-generated displays and flexible timetabling operations in the system. A strong relationship between display formatting and efficacy in interaction is revealed. The second objective was to apply the power of the computer to situations which the manual timetabler finds ‘difficult’. The computer techniques developed from theoretical methods in the literature include infeasibility tests to detect certain problem situations at early construction stages and tree searching methods for interchanging lessons. It is shown that the interactive application of the tree searching methods simplifies the solution of timetabling subproblems which require human decisions on changes to lesson constraints and distribution patterns. The system was successfully used for the preparation of timetables for a high school with a roll of about 1,000 pupils.