Functional grammar may refer to:

• Functional linguistics, a range of functionally based approaches to linguistics
• Functional discourse grammar, grammar models developed by Simon C. Dik that explain how utterances are shaped based on the goals of language users
• Systemic functional grammar, a grammatical description developed by Michael Halliday
• Danish functional linguistics, a strand of functional linguistics associated with linguists at the University of Copenhagen
• Lexical functional grammar, a variety of generative grammar initiated by Joan Bresnan and Ronald Kaplan.
• Role and reference grammar, a model of grammar developed by William Foley and Robert Van Valin, Jr.