The first Earth Day was celebrated in the United States on April 22, 1970. At that time, mainstream America was largely unaware of environmental concerns for clean air, water, and energy. As students nationwide joined the hippie movement and protested the Vietnam War (1959–1975), US Senator Gaylord Nelson (1916–2005) had an idea that helped bring about the modern environmental movement. The first Earth Day led to the formation of the US Environmental Protection Agency and was the catalyst for the passage of the Clean Air, Clean Water, and Endangered Species Acts.

In 1962, marine biologist Rachel Carson released the book Silent Spring, in which she challenges humankind's regard for the natural world. Carson's concerns and warnings stemmed from the broad use of synthetic chemical pesticides after World War II. Although Carson's work received criticism from the chemical industry and some government officials, her book was a New York Times best seller and raised awareness about public health and the ecosystem. Earth Day founder Nelson credits Carson for paving the way for a widespread environmental movement.

Santa Barbara, California, suffered a massive oil spill in 1969. After witnessing the vast damage the spill caused the environment, Wisconsin senator Nelson was inspired to initiate a national, bipartisan movement to raise awareness for environmental concerns. Building upon the energy of student antiwar protestors, Senator Nelson was convinced that he could give environmental protection a national platform. Republican congressman Pete McCloskey and environmental activist Denis Hayes joined in Nelson's efforts. On April 22, 1970, twenty million Americans participated in the inaugural Earth Day. Demonstrators filled streets and parks and college students organized protests. Supporters of the movement crossed all political and socio-economic boundaries. Environmental historians commonly credit Earth Day 1970 as the key turning point in the American public's consciousness about environmental problems. Later that year, the US Environmental Protection Agency was formed, and within three years, a number of federal laws were established to protect and preserve public health and the environment.

The Environmental Protection Agency was established on December 2, 1970, under the administration of President Richard Nixon. His goal was to establish and enforce environmental policy by combining federal research, monitoring, standard-setting, and enforcement activities for the protection of the environment.

The Clean Air Act was signed by President Nixon on December 31, 1970. This federal law protects public health and the environment by regulating the emission of hazardous pollutants into the air. Under the act, the Environmental Protection Agency established National Ambient Air Quality Standards to address public health and welfare concerns caused by air pollutants in each state. Amendments to the act were made in 1977 and 1990 to set additional goals for improving air quality in the United States.

The Federal Water Pollution Control Act had been established in 1948 to regulate quality standards for surface waters (streams, rivers, lakes, and oceans) and the pollutants discharged into those waters. The act was significantly restructured in 1972 and became known as the Clean Water Act. The amendments of 1972 include provisions for a basic protocol for regulating pollutant discharges into US waters, implementation of pollution control programs for wastewater standards, and federal funding for the construction of sewage treatment plants.

The Endangered Species Act was signed by President Nixon on December 28, 1973. The act provides for the conservation of threatened and endangered species, including plants and animals, as well as conservation of the ecosystems upon which endangered species depend. The US Fish and Wildlife Service and the US National Oceanic and Atmospheric Administration Fisheries Service are the federal agencies responsible for implementing the act. Species protected under the act include birds, insects, fish, reptiles, mammals, crustaceans, flowers, grasses, and trees. The US Fish and Wildlife Service oversees and maintains a list of endangered species.

Environmental activist Denis Hayes was asked by environmental leaders to organize another Earth Day campaign in 1990 to celebrate Earth Day's twentieth anniversary. The global campaign involved two hundred million people in 141 countries around the world. Headquartered in Washington, DC, the Earth Day Network has more than 150,000 partners in 192 countries dedicated to expanding the worldwide environmental movement. Each year, more than one billion people participate in Earth Day activities. It is the world's largest civic observance. In 2010, a permanent program was launched in India to enhance the region's environmental movement through leadership and civic involvement. In addition to several environmental programs, Earth Day Network India has launched a multifaceted campaign to reverse the population decline of the endangered Asian elephant.

The Earth Day Network creates environmental engagement opportunities at local and global levels. Since its founding, the Earth Day Network has developed campaigns that raise public awareness on issues ranging from climate change to voter registration. A key focus of the network is to expand the concept of environment so it includes all areas of public health. In addition to reducing air and water pollution, the network creates programs to create green, or environmentally sustainable, practices in communities, schools, and businesses. Modern core network programs include the Green Ribbon Schools Campaign, the Canopy Project, and the Green Cities and Local Governments Campaign.

Earth Day Network partners with the US Green Building Council, the National Wildlife Federation, and the Center for Environmental Literacy to promote green schools and to enhance environmental education. The campaign encourages students to practice environmental responsibility through the use of educational resources and tools provided to teachers and administrators. The Earth Day Network believes that green schools not only conserve resources, but also produce healthier students.

The Earth Day Network developed the Canopy Project to help protect and preserve natural lands by planting trees in impoverished communities around the world. Trees prevent land degradation and are sources of income, energy, and food. Furthermore, trees naturally filter the air, curbing the effects of climate change. Since 2010, tens of millions of trees have been planted in countries including Ethiopia, Kenya, Haiti, the United States, and Norway, with the goal of achieving both economic and environmental sustainability.

Launched in the fall of 2013, the Green Cities and Local Governments Campaign aims to help cities become more sustainable by reducing the greenhouse gas emissions that cause climate change. The campaign's focus is to improve upon the elements of buildings, energy, and transportation to move toward a cleaner and healthier environment. Campaign initiatives include improving building design to reduce greenhouse gas emissions, increasing the use of reusable energy sources such as sunlight and wind, and enhancing public and alternative transportation options.