An event has nondeterministic effects if the event can have two or more alternative effects. For example, flipping a coin has two alternative effects: the coin may land with heads showing, or it may land with tails showing. We represent nondeterministic effects of events in the event calculus by allowing event occurrences to give rise to several classes of models. We describe two ways of representing nondeterministic effects in the event calculus: determining fluents and disjunctive event axioms. These techniques enable the representation of uncertainty about the effects of events.