Mechanical engineering is concerned with the energy, manufacturing, and design of machines. Design, which involves analyzing needs and designing products and systems, including complex human-machine systems, to fill them is key to mechanical engineering.

Mechanical engineers use energy principles and mechanics to design a wide variety of devices, machines, and systems, including complex human-machine systems, for energy conversion, biofuel production, environmental control, materials processing, transportation, materials handling, and other purposes. They may develop robots for space exploration, use a computer to simulate the freezing of human cells, or improve devices for use of alternative energy sources, such as fuel cells, wind turbines, and solar energy converters.