For nearly 40 years, Earth Day has been the one day when even the least eco-minded trade their apathy for (usually) a spade and a tree sapling. From its start as a counter-culture demonstration in 1970--which led to the formation of the EPA and to bills protecting the environment--to the worldwide celebration in 2000 that involved more than 200 hundred million supporters in 184 countries, April 22 means something different to everyone. Figure out which cause you want to support--and how--with the ideas and activities in Planet Green's How to Go Green: Earth Day guide.

1. Choose Your Cause

Whether you'd rather eat local vegetables, clean up a nearby stream, or turn your backyard into a wildlife habitat, Earth Day is the perfect time to start. But before you jump blindly into a project, make sure you're supporting a cause you feel passionate about. Maybe weekend hikes have made you devoted to forests, or summers at the beach encouraged a passion for the world's oceans--whatever it is, your enthusiasm will make the entire process easier and more effective.

2. Deforestation

Go back to the roots of the holiday by fighting deforestation--with more than half the world's tropical forests already demolished, the continuing decline of the tree population leads to everything from global warming to habitat loss. While buying items made from recycled paper or reclaimed wood is a start, you can also use this opportunity to repopulate forests by planting trees or--even better--join a group that will reclaim wood that might otherwise turn into trash.

3. Think Global

If you already devote a large portion of your time to volunteering in your own community, maybe this is a good time to go bigger: look for a volunteer vacation or an eco-tourism trip that will let you leave another location better than you found it. From tracking wildlife to measuring the effect of climate change on glaciers, you'll be able to see the world while making sure it lasts as long as possible.

Planet Green's Guide: How to Go Green: Earth Day