This monograph presents a theory of ellipsis licensing in terms of Agree and applies it to several elliptical phenomena in both English and Dutch. The author makes two main claims: The head selecting the ellipsis site is checked against the head licensing ellipsis in order for ellipsis to occur, and ellipsis - i.e., sending part of the structure to PF for non-pronunciation - occurs as soon as this checking relation is established. At that point, the ellipsis site becomes inaccessible for further syntactic operations. Consequently, this theory explains the limited extraction data displayed by 'Dutch modals complement ellipsis' as well as British English do: These ellipses allow subject extraction out of the ellipsis site, but not object extraction. The analysis also extends to phenomena that do not display such a restricted extraction, such as sluicing, VP ellipsis, and pseudogapping. Hence, this work is a step towards a unified analysis of ellipsis.