Motility is a biological term which refers to the ability to move spontaneously and actively, consuming energy in the process. It can apply to either single-celled or multicellular organisms. Motile marine animals are commonly called free-swimming. The opposite of motility is sessility. Examples of motility include:

• Sperm cells, propelled by the regular beat of their flagellum
• The bacterium E. coli, which swims by roting a helical prokaryotic flagellum

In cellular biology or biomedical engineering, motility often refers to directed cell movement down gradients established in biopolymers. Examples include:

• movement along a chemical gradient (see chemotaxis)
• movement along a temperature gradient (see thermotaxis)
• movement along a light gradient (see phototaxis)
• movement along a magnetic field line (see magnetotaxis)
• movement along a electric field (see galvanotaxis)
• movement along the direction of the gravitational force (see gravitaxis)
• movement along a rigidity gradient (see durotaxis)
• movement along a gradient of cell adhesion sites (see haptotaxis)

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