This chapter examines three themes concerning ellipsis that have been extensively discussed in transformational generative grammar: structure, recoverability, and licensing. It reviews arguments in favor of the analysis according to which the ellipsis site is syntactically fully represented, and compares the two variants of this analysis (the deletion analysis and the LF-copying analysis). It is concluded that the deletion analysis is superior to the LF-copying analysis. A discussion of recoverability follows, which concludes that in order for elided material to be recoverable, a semantic identity condition must be satisfied, but that is not a sufficient condition: syntactic or formal identity must be taken into account. The chapter finally considers licensing. It reviews some proposals in the literature about what properties of licensing heads and what local relation between the ellipsis site and the licensing head are relevant to ellipsis licensing.