The work reported in this thesis is concerned with both a fundamental assessment and the provision of a comprehensive MDI system for milling machines. The conceptual design has led to the realisation of a prototype work station which represents advances beyond the current state of the art for systems containing an APT-like processor and employs a powerful and flexible conversationally-based system with graphics support. The work station has been interfaced in STR mode to a numerically controlled milling machine and the effectiveness of the programming system has been demonstrated by the production of four workpieces.