The Sapir-Whorf hypothesis, the theory that language influences thought to the extent that people who speak different languages perceive the world differently, is discussed in the context of current calls to maintain and promote global linguistic diversity. Cross-cultural psychological research is examined to assess the extent to which the hypothesis can be shown to be true. In the 1970s, research on colour perception appeared to provide evidence against the hypothesis. More recent studies have shown that there are in fact significant and reliable differences across languages in how colour is perceived, classified, and remembered. Research at higher levels of language is also assessed. Language appears to exert considerable influence over how people categorise, evaluate, and remember the world, especially in languages where nouns belong to different semantic categories. Particular ways of thinking may also be more difficult in some languages than others. This may only mean that it is more cognitively taxing to arrive at the same notion or it can mean that an idea is highly unlikely to be expressed in a particular language. These differences may even transcend languages and cultures. It is concluded that, given the available evidence, it is vital to allow alternative perspectives of the world to be available by maintaining and promoting global linguistic diversity.