This paper presents a corpus-based analysis of verb agreement in English wh-clefts. The copula in wh-clefts displays a number agreement alternation if the focused element is a plural noun phrase, as in What we want is/are more books in the library. Pedagogical grammars that address this variation hold opposing views on which of the two variants is preferred in formal English. To resolve this issue, the research for this paper examines the entire British National Corpus. An analysis of the present-tense copulas in the relevant wh-cleft constructions reveals that singular agreement is the predominant choicethe author's analysis found 328 occurrences of singular (61.3%) versus 207 occurrences of plural (38.7%). However, in academic prose, the most formal register, the plural copula occurs slightly more frequently (56.6%) than the singular copula (43.4%). The preference for plural verb agreement in academic prose resembles the agreement pattern of there-constructions.