Google Maps is designed mostly for directions. Added bonus: it has satellite and terrain imagery.

Google Earth, on the other hand, is designed to view the globe in a 3-dimensional kind of way, with the added benefit of driving directions.

For example, you start with your view of earth from space, and when you type in a location, Google Earth will "fly" you to that location. In addition to just panning left and right from the viewpoint of directly over the top of the subject, you can also tilt the map such that the view is as if you were floating above ground and looking out at the horizon. When looking at mountains in this way, you can get a sense of just how tall a mountain is, for example. Perhaps the best example is to take a trip to Niagra Falls and tilt the map up and down, then rotate around niagra falls to get the complete experience.

Google Earth also has much more *data* about the places you're looking at. For example, you can overlay pictures from the past to see changes in the environment, you can see Wikipedia or Panoramio pictures that have been taken/tagged at that location, as well as other data like finding parks, restaurants, etc. all without searching. They just appear.

At the core of all this functionality is the idea of layers. You can add and remove as many layers as you wish. Referencing the example above, I might have the Parks, Restaurants, and Panoramio layers all turned on. If I didn't want to see the Restaurants in my area, I could simply turn that layer off.

Another cool thing about Google Earth is exploring cities that have a 3D buildings layer. Fly to, say, San Francisco, then turn on the 3D buildings layer. You can then take a virtual tour of San Francisco in a much more meaningful way--cruising in between sky scrapers and through the cables of the Golden Gate or Bay Bridge--than you could with a top-down view from Google Maps.

Most of us use it for fun and exploration, but some people/organizations use it for serious work, too, especially those in the environment industry.

Navigation is the main distinction to me. If I want to look at different cities around the globe then Google Earth makes this easier and faster then Google Maps. If I just want directions or to quickly look at a road map then I use Google Maps. If I want to zoom in on major cities in Japan and parts of Europe and do it quickly then I use Google Earth. Also, if you want to learn geography then Google Earth is better since it renders the entire globe in 3D which is way more accurate then any flat map can do. Also you can use many more layers in Google Earth that are not available in Google Maps. Many buildings in Google Earth are also redered in 3-D, So is terrain like mountains. Playing around with varied layers is more interesting to me then most other things about Google Earth.

Google Earth has waayy more features.