The Environmental Science Activities for the 21st Century (ESA21) project provides multi-week activity modules around major topics in environmental science. The modules are designed to supplement environmental science courses with existing laboratory components or provide course activities for traditional and online courses that lack a laboratory component. The activities hybridize online and wet-lab exercises to take advantage of both formats and utilize existing, high-quality materials from the Internet. The modules emphasize lifestyle examination, ethical considerations and critical analysis of individual contributions to large-scale regional and global impacts. This allows students to see their place in the environment and how lifestyle changes can facilitate greater environmental sustainability. Modules cover the atmosphere, basic science, biogeochemical cycles, energy, fossil fuels, nuclear energy, ozone, renewable energy and water.