This chapter describes the current state of the art in altmetrics research and practice. Altmetrics—evaluation methods of scholarly activities that serve as alternatives to citation-based metrics—are a relatively new but quickly growing area of research. For example, researchers are expecting that altmetrics that are based on social media data will reflect a broader public´s perception of science and will provide timely reactions to new scientific findings. This chapter explains how altmetrics have emerged and how they are related to the academic use of social media. It also provides an overview of current altmetric tools and potential data sources for computing alternative metrics, such as blogs, Twitter, social bookmarking services, and Wikipedia.