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. Presents some of the key ideas and innovations in earlier research that have been driving the evolution from bibliometrics to webometrics, and with the advent of social media to altmetrics Discusses the shortcomings and pitfalls of bibliometrics in research evaluation and the potential of altmetrics to overcome some of these shortcomings Presents some of the most important data sources of altmetrics, the aggregators, and the different stakeholders Reviews current research about altmetrics and discusses possible future trends Presents a way to measure and aggregate altmetrics according to the level of impact or type of impact they represent