 After a short introduction to basic notions of tense and aspect we briefly discuss temporal logic, and then Reichenbach’s famous distinction between speech time, event time and reference time. Event-based semantic theories treat events as ontological primitives, so in the following section we show how time can be constructed from event structures, as exemplified by the Russell-Kamp construction. These sections are followed by a discussion of the most important observations concerning lexical and grammatical aspect, including the famous imperfective paradox. Next we introduce two widely discussed theories of temporality and show how they cope with the imperfective paradox. This section is followed by one that shows how temporal information is expressed in Artificial Intelligence (AI). We use the event calculus from AI to present a solution of the imperfective paradox, by viewing it as an instance of the frame problem. The last section is devoted to gathering psycholinguistic evidence showing that at least some of the philosophical and semantic concepts discussed in this article may be cognitively real. 