Core cases of agreement can be characterized as morphological marking on the central verb of a clause that reflects some features of a noun phrase in that clause. Virtually all generative treatments begin with subject-verb agreement, for reasons that are easy to understand. First, this is the most common kind, being found in almost 75 percent of languages sampled, whereas object agreement is only found in some 50 percent. In addition to changing perspective on the structural conditions on agreement, Chomsky also inverted the relative importance of agreement and case within generative syntax. The role of case theory is now often backgrounded, and case is seen as an additional side effect of the primary relation of Agree. The agreement and case are lively areas of ongoing inquiry, an integral part in one way or another of the larger generative enterprise.