An adverb clause is a subordinate clause that functions like an adverb by providing information about time, place, manner, cause, condition. Adverb clauses can occur in different positions within a sentence and are usually preceded by a comma only when they begin a sentence. Adverb clauses are introduced by subordinating conjunctions like after, although, before, because, if, unless, when, which indicate the relationship between the adverb clause and the word it modifies.