This thesis seeks to reexamine the theoretical principles of individualised instruction against the background of computer assisted instruction. It demonstrates that these principles can be adhered to in designing programs employing microcomputers in teaching foreign languages. The study reviews the theoretical considerations in computer assisted instruction and indicates some of the advantages and limitations of using computers in foreign language teaching. Five documented studies are outlined to demonstrate how theory is put into practice, and the study discusses such factors as the reduction of drudgery in the classroom, the humanisation of classroom teaching, error analysis, compilation of item banks and student reaction to computer assisted instruction. The study concludes with a reminder that the computer is still only a tool and should never be seen as anything more than an ancillary to a competent human teacher.