  Social media metrics - commonly coined as "altmetrics" - have been heralded
as great democratizers of science, providing broader and timelier indicators of
impact than citations. These metrics come from a range of sources, including
Twitter, blogs, social reference managers, post-publication peer review, and
other social media platforms. Social media metrics have begun to be used as
indicators of scientific impact, yet the theoretical foundation, empirical
validity, and extent of use of platforms underlying these metrics lack thorough
treatment in the literature. This editorial provides an overview of terminology
and definitions of altmetrics and summarizes current research regarding social
media use in academia, social media metrics as well as data reliability and
validity. The papers of the special issue are introduced.
