A reader wrote asking about the correct use of the relative pronouns that and which. I give quite a number of examples of their use in relative clauses but had overlooked listing the rules governing their use. I’ve now added that information to the Pronoun Problems page under the heading Relative Pronouns: That, Which, Who, Whose, Whom.
For punctuating relative clauses see Restrictive and Non-Restrictive Modifiers in the Punctuation section.
I warmly recommend the excellent full discussion of relative pronouns in Wikipedia under “English Relative Clauses”.