This paper argues for the need to recognize a new order of syntactic phenomena, and for a theory of syntax capable of addressing it. Dialogic syntax encompasses the linguistic, cognitive, and interactional processes involved when speakers selectively reproduce aspects of prior utterances, and when recipients recognize the resulting parallelisms and draw inferences from them. Its most visible reflex occurs when one speaker constructs an utterance based on the immediately co-present utterance of a dialogic partner. Words, structures, and other linguistic resources invoked by the first speaker are selectively reproduced by the second. The alignment of utterances yields a pairing of patterns at varying levels of abstraction, ranging from identity of words and affixes, to parallelism of syntactic structures, to equivalence of grammatical categories and abstract features of form, meaning, and function. This mapping generates dialogic resonance, defined as the catalytic activation of affinities across utterances. The key unit of analysis is the diagraph, recognized as a higher-order, supra-sentential syntactic structure that emerges from the structural coupling of two or more utterances. Dialogic syntax goes beyond traditional linear syntax to recognize as integral to the task of syntactic analysis a new kind of structural relation that arises between otherwise independent sentences.