While it is generally agreed that an elliptical Verb Phrase must be identical to its antecedent, the precise formulation of the identity condition is controversial. I present a semantic identity condition on VP ellipsis: the elided VP must have the same meaning as its antecedent. I argue that a semantic identity condition is superior to a syntactic condition on both empirical and theoretical grounds. In addition, I show that the proposed condition differs significantly from previously proposed semantic conditions, in that other approaches do not take into account the dynamic nature of semantic representation.