A periodic sentence is a sentence that is not grammatically complete until its end. Periodicity is accomplished by the use of parallel phrases or clauses at the opening or by the use of dependent clauses preceding the independent clause; that is, the kernel of thought contained in the subject/verb group appears at the end of a succession of modifiers. It is the opposite of a nuclear sentence.

This type of sentence was created by Isocrates, an Ancient Greek rhetorician. Today, the term "period" denotes the punctuation mark that the Britons call a full stop.