The paper is a response to the surprise with which some policy makers responded to news that greening had been detected in the Sahel. It first views Sahelian environmental change and related policies through the lenses of scientific models of pastoral and agricultural systems. For pastoralism, the lenses are models of equilibrial ecology, those of state-and-transition and those of more recent development. For agricultural systems, they are models of commercialization, modernization and degradation, and those that stress the endogenous development of peasant agriculture. The conclusions are that little, if any, of the recent greening, if and where it has occurred, could be attributed to policy; and that as yet neither models nor interpretations of the satellite imagery yet give firm guidelines for policy. Nonetheless, the review suggests a lesson for the development of policy: it needs to be more dynamic, and in three contexts: (1) the contingencies of pastoral and agricultural economies; (2) continual and sometimes drastic changes in the environment; and (3) changes in political, social, economic and scientific ideas. But policy must retain consistency, and be attuned to the global as well as to local context.