Waiting for Godot by Samuel Beckett is neither fully a tragedy or a comedy in the classical sense, but rather an experimental play belonging to a genre known as "absurdist" theatre that self-consciously breaks down and challenges the traditional generic conventions.
In Aristotle's classical definition of the two genres, comedy is about people worse than average (rustics, buffoons, misers, cuckolds, etc.), and tragedy about people greater than average (kings, queens, heroes). Renaissance drama was the beginning of the genre in which comic interludes occur in tragic plays, where rustics such as the gravediggers in Shakespeare's Hamlet provide "comic relief". Similarly, one could argue that Pozzo and Lucky, representing the aristocrat and the intellectual, are "tragic" heroes (especially in their fall from the first to the second appearance) and Vladamir and Estragon "rustics" or comic elements, except that all four characters are portrayed parodically, rather than conforming to generic norms. This shifting back and forth between comic and tragic elements is expressed in the quotation:
"The tears of the world are a constant quantity. For each one who begins to weep somewhere else another stops. The same is true of the laugh. Let us not then speak ill of our generation, it is not any unhappier than its predecessors. Let us not speak well of it either. Let us not speak of it at all. It is true the population has increased."