Whilst the traditional sciences have been recognised for decades, it was only with the emergence of serious environmental problems in the mid-20th century that environmental science was professionalised. But now, a minor revolution is taking place and the environmental sciences are leading the way. In the last few years, the introduction of portable technologies such as GPS and image processing has allowed curious non-experts, ‘citizens’, to get involved, collecting data with little more than a smartphone. This, along with social media connecting people worldwide, means that researchers can be aided by large, widespread teams. Citizen science does however have its critics, who question data quality or participant motivation. This issue highlights examples of exciting and innovative citizen science successes, but also seeks to address some of these concerns.