Also 'illocutionary act theory'.
Originally formulated by the British philosopher John Langshaw Austin (1911-1960), and developed by the American JOHN ROGERS SEARLE (1932- ), it is a branch of PRAGMATICS.
When saying something, one is simultaneously doing something. An 'utterance act' is performed in voicing words and sentences; a 'propositional act' is carried out by referring to entities and predicating states and actions.
The interpersonal act performed in speaking is an 'illocutionary act' (the central concept): 'I promise to pay you $5.00' counts as an act of promising if certain SINCERITY CONDITIONS or FELICITY CONDITIONS are fulfilled.
The intended effect on the addressee is a 'perlocutionary act'.
J L Austin, How to Do Things with Words (Oxford, 1962);
J R Searle, Speech Acts (Cambridge, 1969)