Robots can be placed into roughly two categories based on the type of job they do:

Jobs which a robot can do better than a human. Here, robots can increase productivity, accuracy, and endurance.

Jobs which a human could do better than a robot, but it is desirable to remove the human for some reason. Here, robots free us from dirty, dangerous and dull tasks.

Manipulation

Robots which must work in the real world require some way to manipulate objects; pick up, modify, destroy or otherwise have an effect. Thus the 'hands' of a robot are often referred to as end effectors, while the arm is referred to as a manipulator. Most robot arms have replacable effectors, each allowing them to perform some small range of tasks. Some have a fixed manipulator which cannot be replaced, while a few have one very general purpose manipulator, for example a humanoid hand.

Grippers: A common effector is the gripper. Usually it consists of just two fingers which can open and close to pick up and let go of a range of small objects.

Vacuum Grippers: Pick and place robots for electronic components and for large objects like car windscreens, will often use very simple vacuum grippers. These are very simple, but can hold very large loads, and pick up any object with a smooth surface to suck on to.

General purpose effectors: Some advanced robots are beginning to use fully humanoid hands, like the Shadow Hand (right), or the Schunk hand. These highly dexterous manipulators, with as many as 20 degrees of freedom and hundreds of tactile sensors can be difficult to control. The computer must consider a great deal of information, and decide on the best way to manipulate an object from many possibilities.

Locomotion

For simplicity, most mobile robots have wheels. However, some researchers have tried to create more complex wheeled robots, with only one or two wheels.

Two-wheeled balancing: While the Segway is not commonly thought of as a robot, it can be thought of as a component of a robot. Several real robots do use a similar dynamic balancing algorithm, and NASA's Robonaut has been mounted on a Segway.

Ballbot: Carnegie Mellon University researchers have developed a new type of mobile robot that balances on a ball instead of legs or wheels. "Ballbot" is a self-contained, battery-operated, omnidirectional robot that balances dynamically on a single urethane-coated metal sphere. It weighs 95 pounds and is the approximate height and width of a person. Because of its long, thin shape and ability to maneuver in tight spaces, it has the potential to function better than current robots can in environments with people.

Walking is a difficult and dynamic problem to solve. Several robots have been made which can walk reliably on two legs, however none have yet been made which are as robust as a human. Typically, these robots can walk well on flat floors, can occasionally walk up stairs. None can walk over rocky, uneven terrain.