This document provides an overview of altmetrics, which are alternative metrics to traditional citations for measuring the impact of scholarly works. It discusses what altmetrics are, who the major players are in the altmetrics field, when altmetrics data is available, where altmetrics are relevant, why altmetrics are gaining importance, and how altmetrics data is collected and used. The document aims to give the reader a comprehensive introduction to the concept of altmetrics for evaluating scholarly impact and engagement.