Over the past fifteen years social media has transformed our social lives, communications and business. In this guidance note we explore how social media can support environmental monitoring and research, and how its potential can be realised. We explore why social media is valuable e.g. a huge amount of ‘real time’ data, opportunities for increased engagement and gaining information on people’s interactions with their environment. We also explore its challenges, including the technicalities (and ethics) of collating and re-using data from social media sites and issues of data quality and bias. Six Case Studies, from a symposium organised by the UKEOF Citizen Science Working Group (www.ukeof.org.uk/our-work/citizen-science), show how this has been put in practice. We hope that this will facilitate further discussion and collaboration on the use of social media for environmental monitoring and research.