The respiratory system is a biological system comprising of particular structures and organs utilized for gas exchange. The voice box, nose, windpipe, mouth, lungs and throat are part of the respiratory system. It is negatively affected by infection, aging, allergies, asthma and other conditions causing inflammation. These infections can be further divided into lower respiratory tract infections (LRTI) or upper respiratory tract infections (URTI). A few of the upper respiratory tract infections are epiglottitis, common cold, laryngotracheitist and sinusitis. Major lower respiratory tract infections are bronchitis, pneumonia and bronchiolitis. The most common bacterial pathogens causing the lower and upper respiratory tract infections are Moraxella catarrhalis, Streptococcus pneumonia and Haemophilus influenza. This book contains some path-breaking studies on the topic of respiratory system infections. It presents researches and studies performed by experts across the globe on the microbiology of these infections. This book will help new researchers by foregrounding their knowledge in respiratory system infections.