It has been 41 years since the late Wisconsin Senator Gaylord Nelson launched the first nationwide grassroots demonstration on behalf of the environment, known as Earth Day. The event was a national "teach-in" about environmental causes, and it is widely considered the spark that ignited the modern environmental education movement. Within months, President Nixon passed the National Environmental Education Act, and a new subject was introduced into the curricula of K-12 schools across the country. Four decades later, educators have access to a wealth of online resources for green teaching and learning. Some are intended specifically for K-12; others are educational resources without a K-12 focus. All of them are worth considering. This article presents some examples of online tools that can help educators inform and instruct their students about environmental issues.