This document provides information about relative clauses, which are clauses that contain a relative pronoun like who, where, that or which. It explains that relative clauses can be either defining or nondefining. Defining relative clauses add essential information to a sentence that cannot be understood without the clause. Nondefining relative clauses provide extra information to a sentence using commas, and the sentence can still be understood if the clause is removed. Examples of defining and nondefining relative clauses are given to illustrate the differences.