As linguists, we know that language matters. But to many people it might come as a surprise to realize that when students begin their university life, some of their main problems are linguistic ones. When students fail to communicate with professors in an appropriate register, or allow the relaxed style of a lecture to disrupt the formality of a term paper, they are falling into linguistic traps for which no one has prepared them. For non-native speakers, the difficulties may be particularly acute, but even for natives, mastering a range of new registers can pose serious difficulties. Yet this problem often passes unnoticed, perhaps because people are almost as oblivious to language as to the air they breathe or because tools have not been available to research the situation objectively.