Model Based Animation

Model based animations are made with different materials the most commonly used Plasticine clay, the clay is used to make all the characters whether human or animal, there is a freedom to what can be made in claymation. All the things that are made using the clay are "deformable". This means that because they are made from a malleable substance they can be easily changed and morphed into different things, you could change a policeman into a shark if you wanted. 
Each object or character is usually around a wire skeleton called an armature, and then arranged on the set, where it is photographed once before being slightly moved by hand to prepare it for the next shot, and so on until the animator has achieved the desired amount of film. Upon playback the illusion it created tricks the human eye so it looks like real time movement.

The most famous example of claymation works are all productions done by Aardman animations, the British company that was founded in 1972 and has made over  $894 million world wide from their films. The most famous example of Aardman Animations work would be the long running TV series and movie Wallace And Gromit.

Here is a 20 minute video on how Aardman studies makes their work, it has some great information on the claymation community of animators. 

Model Based Animation  films were produced in the United States as early as 1908, but didn't become popular until; 1916 when East Coast artist named Helene Dayton and a West Coast animator named Willie Hopkins produced clay-animated films on a wide range of subjects, with Hopkins producing over 50 model based animated sequences.