• Rationality, a concept of reason
• Rational number, a number that can be expressed as a ratio of two integers
• Rational function, a mathematical function which can be written as the ratio of two polynomial functions
• Rational Software, formerly Rational Software Corporation, a software company now owned by IBM
• a central paradigm of Rational Emotive Behavior Therapy
• one of the four temperaments according to the Keirsey Temperament Sorter
• Rational choice theory, a theoretical paradigm in microeconomics

See also

• Rationalism (disambiguation)
• Rationale, a liturgical vestment worn by clergy