This document summarizes defining and non-defining relative clauses in English. It explains that defining relative clauses identify a specific person or thing, while non-defining clauses provide additional information. It provides examples of relative pronouns like "who", "which", "that", "whose", "where", and "when". It also discusses when these pronouns can be omitted and which cannot be used in defining vs. non-defining clauses. The document concludes by instructing students to practice these concepts in exercises in their book.