Comprising 12 chapters, this book focuses on volatile methylsiloxanes (VMSs), the shorter-chained organosiloxanes, and reviews the main areas and environmental compartments where they have been found and studied. It opens with a detailed description of the structural and functional properties, toxic risks and possible transformations of VMSs in the environment and their main uses in various activities and products, as well as the identification of the main sources of emission. Further chapters examine the analytical strategies and protocols that have been used to address the quantification of VMSs, including the issue of possible cross-contaminations. The book also discusses the presence of VMSs in wastewater treatment plants (WWTPs) and in water bodies, their atmospheric fate and levels in biota, as well as occurrences of VMSs in remote areas of the world. It closes with a comprehensive conclusion and discussion on future directions for upcoming studies. This book is not intended as a finishing line, but rather as an important step towards improving our understanding of VMSs, to fuel new collaborations between research groups and/or with industry and lastly to convince more researchers to explore the mysteries of these ubiquitous, yet understudied, chemicals.