During the recent years, there has been a tendency to switch over from hardware based teaching material to software based systems. In this process fewer students are getting exposed to hardware based systems and development of teaching material based on hardware contents. With the recent developments in optoelectronics and a variety of devices now available, especially light-emitting diodes of different colours and sizes, teaching aids based on LEDs offer distinct advantages. They are attractive, dynamic, easily integrated with other semiconductors and a single model can convey more information – easily understood - than several pages of text material. Furthermore, they are ideally suited for science exhibitions and displays. This book covers the basic principles underlying the design and fabrication of a variety of models in basic physics, chemistry and biology. Details of electronic circuits and the mechanical assemblies of ten models are provided. This should provide sufficient material for enthusiasts to develop their own models according to their particular requirements. The book is intended for high school and undergraduates students in science and engineering faculties.