In this introductory chapter which sets the scene for this book, the background which stimulates this research work is first provided. The motivation for the focus of the work is then explained, highlighting the importance of the breath analysis used in disease diagnosis, of the development of breath analysis device, and of the design of specific pattern recognition algorithm for breath analysis. This is followed by a statement of the objective of the research, a brief summary of the work, and a general outline of the overall structure of the present study.