The goal of any research assessment is to evaluate the value or quality of the research in comparison to other research. As quality is highly subjective and difficult to measure, citations are used as a proxy. Citations are an important part of scholarly communication and a significant component of research evaluation, with the assumption being that highly cited work has influenced the work of many other researchers and hence it is more valuable. Recently we have seen new online data sources being researched for this purpose and disruptive ideas with the power to change research assessment, and perhaps even science as a whole, have been born. Altmetrics is the new research area that investigates the potential of these new data source as indicators of the impact that research has made on the scientific community and beyond, and thus possibly also as indicators of the societal impact of research. This book will present some of these new data sources, findings from earlier altmetrics research, and the disruptive ideas that may radically change scholarly communication.