First of all, try scrolling up and down thing page. Use your scroll wheel, use the scroll bar, use the arrow keys, page up, page down, space bar. Note how the text scrolls normally, but the green background scrolls slowly, and how the clouds scroll faster than normal. That's the parallax effect. You can make as many layers parallax as you desire, or as many as your browser can render fast enough to keep the effect alive. It works best in Safari, and Firefox if you have Smooth Scrolling enabled. Source : http://inner.geek.nz/javascript/parallax/