Social media are becoming more and more popular in scientific communication. Scientists use them for a range of purposes, from sharing publications, to blogging about their own or others’ research, conference tweeting, interpersonal communication and online participation, for example via Q&As on academic social network sites like ResearchGate and academia.edu. Moreover, many social media platforms can be used for impact measurement via so-called altmetrics. Altmetrics capture and aggregate social media metrics such as (re)tweets, Facebook likes, Mendeley bookmarks and Wikipedia cites. They can challenge or at least complement bibliometric impact measures, like the Journal Impact Factor and the h-index, which have been criticized on various grounds. This presentation first summarizes recent studies on social media adoption in science. It then focuses on altmetrics and summarizes key findings in that domain. Finally, it gives a hands-on introduction to altmetrics by demonstrating two prominent services: Impactstory and Altmetric.com.