It's co-ordinated globally by the not-for-profit organisation Earth Day Network, and has become the largest secular celebration on the planet. You can find out what's happening in your area on their website: http://www.earthday.org/.
I know there are lots of climate-change doubters out there, and folk who challenge the science on all of this. I'm not really qualified to argue with them, but it seems to me to be an issue that's just too big for us to gamble on. The downside of getting it wrong, for the sake of our children and the world we leave behind, is just too terrible to think about.
So for Earth Day 2016 here's my own little collage of favourite moments from the last 12 months, by way of celebrating Mother Earth and her rich bounty.
All the best for now and Happy Earth Day!