In fewer than twenty-four hours from now, the full moon will pass through earth's shadow to create a total lunar eclipse. The next one will not take place until April 2014.
This previous post on the phases of the moon explains why lunar eclipses occur at full moons and why solar eclipses occur at new moons. This post contains some other drawings which may be of additional assistance in understanding the mechanics of the moon's orbit and interaction with the earth and the sun from the perspective of viewers on earth.
This previous post explains how the fact that the orbital plane of the moon is tilted at a 5.1o angle to the plane of the ecliptic (the plane upon which earth, and the other planets to a greater or lesser degree, orbit the sun) creates the two "lunar nodes." These nodes are located where the two planes intersect, and this fact of the offset orbital planes explains why lunar and solar eclipses do not occur every month. The total lunar eclipse that is approaching will take place when the full moon passes through a lunar node, intersecting with the ecliptic plane.
The upcoming eclipse will be visible for observers in the parts of the world shown in the NASA map below.
For some excellent additional discussion and information about this exciting upcoming heavenly event, see the Urban Astronomer blog (which explains viewing details for the west coast of the United States and Canada), the NASA website, and this article from Sky & Telescope.