Not to be confused with the Roman number III.

Ill (ill) may refer to:

• to suffer from an illness or disease
• Ill (Austria), a river in western Austria
• Ill (France), a river in north-eastern France
• Illinois, often abbreviated Ill.

ILL may stand for:

• Institut Laue-Langevin, a scientific research facility in Grenoble, France
• Interlibrary loan, a service offered by libraries that wish to share their materials
• Institute of Linguists (London)
• I Love Lucy