The sense of smell is one of our fundamental senses. Detection of smell plays vital role in wide range of industrial and domestic applications. Olfaction is a challenging new sensing modality for intelligent systems. With the emergence of electronic noses (e-noses) it is now possible to train a system to detect and recognize a range of different odours. An electronic nose (e-nose) is an intelligent sensing device that uses an array of gas sensors of partial and overlapping selectivity along with a pattern recognition component to distinguish between both simple and complex odours. To date, e- noses have had a variety of use in a number of applications from the food industry to medical diagnosis. In this book, I have integrated the electronic nose working principle, sensors used for E-nose and overview of applications of E-nose. For beginners as well researchers this book is a brief guide of E-nose.