Relative pronouns in Catalan grammar are essential for connecting clauses and providing more information about the antecedent. These pronouns help to modify and specify the meaning in a sentence. Some of the common relative pronouns in Catalan grammar include ‘que’, ‘qui’, ‘el qual’, ‘la qual’, ‘els quals’, ‘les quals’, ‘on’, and ‘d’on’. By mastering relative pronouns, learners of the Catalan language can improve their language proficiency and create complex sentences with ease.