On the basis of five case studies from languages of the American Pacific Northwest, we argue that, at least in the areas of syntax and semantics, a scientific approach to the study of linguistic diversity must be empirically grounded in theoretically informed, hypothesis-driven fieldwork on individual languages. This runs counter to recent high-profile claims that large-scale typology based on the sampling of descriptive grammars yields superior results. We show that only a hypothesisdriven approach makes falsifiable predictions, and only a methodology that yields negative as well as positive evidence can effectively test those predictions. Targeted elicitation is particularly important for languages with a small number of speakers, where statistical analysis of large-scale corpora is impossible. Given that a large proportion of the world's linguistic diversity is found in such languages, we conclude that formal, hypothesis-driven fieldwork constitutes the best way rapidly and efficiently to document the world's remaining syntactic and semantic diversity.* 1. Introduction. At least half of the world's nearly 7,000 languages will no longer be spoken by the end of this century (Harrison 2007, among many others). This imminent large-scale language extinction has alarming consequences for the investigation of linguistic diversity. If we wish to understand the scope and limits of crosslinguistic variation, it is imperative that in the near future we gather as much information about endangered languages as we can, in a form that allows systematic and accurate crosslinguistic comparison.The need for such work is accepted by linguists of all persuasions; more controversial is how we should go about it. The difficulty of the task is compounded by the fact that nearly all endangered languages are spoken by small and aging populations, and many have already fallen into disuse even among those who speak them fluently. These circumstances pose unique challenges for fieldworkers, who must find the most effective way to probe for linguistic diversity in the limited time frame still available.In this article we present, illustrate, and defend a methodological approach for detecting linguistic diversity in the areas of syntax and semantics. Our method consists of hypothesis-driven research on a range of languages. Data collection is driven by the need to test the predictions of formal hypotheses, and data are gathered primarily (but not exclusively) by means of fieldwork carried out over an extended time period with a small number of speakers.