A restrictive relative clause (RRC hereafter), which is also known as a defining relative clause, gives essential information about a noun that comes before it: without this clause the sentence wouldn’t make much sense. A RRC can be introduced by that, which, whose, who, or whom. Givon (1993, 1995), Fox (1987), Fox and Thompson (1990) state that a RCC is used for two main functions: grounding and description. When a RRC serves the function of linking the current referent to the preceding utterance in the discourse, it does a grounding function; and when the information coded in a RRC is associated with the prior proposition frame, the RRC does a proposition-linking grounding function. Furthermore, when a RRC is not used to ground a new discourse entity, the purpose of it is to provide new information for its newly-introduced head NP. RRC of this kind perform a description function. Based on empirical analyses of 10 letters to editors, the present study investigates the use of RRCs in written text. The study draws on Givon (1993, 1995), Fox (1987), Fox and Thompson (1990) classification of RRCs' functions as outlined above. The analysis of data reveals that the use of RRCs as performing the grounding function is intuitively clear in letters to the editors. By comparison, the description function of RRCs is less than the grounding function and it varies between makes assertion about its head NPs and provides information for the newly-introduced NP. That is, in some cases RRC only makes assertion about its head NP without necessarily provides information for the newly-introduced NP and vice versa. The study further finds out that the third kind of grounding, which is done by the main clause instead of relative clauses, is impossible function of RRCs in letters to the editors