Time adverbials introduced by until impose restrictions on the aspectual class of the main clause they combine with: they only combine with durative sentences. In negative sentences, the situation is more complex. The question arises whether negative sentences are durative, or whether there is a separate use of until as a negative polarity item. In this paper, I discuss the three treatments of not…until that are characterized in the literature as the scope analysis, the ambiguity thesis and the lexical composition approach. I work out the interpretation of the three approaches in an event-based semantics, and argue that they are truth-conditionally equivalent in sentences containing an explicit negation. Furthermore, they generate the same pragmatic implicatures. A seperate negative polarity use of until is motivated by sentences containing NPI-licensers different from explicit negation, though. The observation that the scope analysis, the ambiguity thesis and the lexical composition approach are semantically and pragmatically equivalent in sentences containing an explicit negation helps us describe the similarities and differences between the expression of exclusion of a range of values on the time axis in a variety of languages.