The easiest place to see the differences is also usually the first place observed with these animals - their head. There are several fairly easy differences between crocodiles and alligators visible on their heads.
Alligators have snouts that are shaped more like a U, not as pointed as those of crocodiles. Alligator heads tend to be wider and shorter. The teeth in the lower jaw of an alligator fit into spaces in the upper jaw when the mouth is closed since the upper jaw is wider than the lower jaw.
Crocodiles have longer, more pointed, V-shaped snouts. There is no difference in width between the upper and lower jaws of crocodiles; lower jaw teeth lie around the outside edge of the upper jaw when the mouth is closed.
Alligators are generally darker in color than are crocodiles, although this may be difficult to determine depending on water clarity. Crocodiles have a "jaagged fringe" of skin on the hind feet and legs; alligators do not have this feature. The hind toes of alligators are webbed, unlike crocodile toes.
Alligators prefer fresh water, while crocodiles prefer salt water. Both species can live in either type of environment. Crocodiles tend to be more aggressive than alligators.