Over the past few decades, soft tissue augmentation has become an increasingly popular procedure, not limited to a specific age or sex group. It is not only utilized in beauty restoration but recently it has been found useful in treating different developmental defects. A wide range of products are available on the market today. Hyaluronic acid fillers, made from hyaluronic acid (a naturely occuring biopolymer) are one of the most commonly used fillers, owing to their nonimmunogenicity, biocompatibility & unique advantage of being reversible. This book provides a brief account of soft tissue augmentation and a more detailed presentation of hyaluronic acid, its biology, chemistry, advantages, disadvantages and other interesting facts. The purpose of this research was to shed a light on the histological & immunological effects of hyaluronic acid fillers on soft tissue, namely buccal mucosa. It also provides an in-depth discussion of possible theories that may have led to such results. This should be useful & informative to the patient, surgeon and the product manufacturer, to help in the innovation and development of a product that could bring us closer to the ideal filler material.