Scientists assist protected area managers by developing information and knowledge that can be used to better monitor and manage recreation use and its impacts. Most recreation management decisions have both a descriptive and an evaluative component. There is widespread consensus that science is well suited to discovering, synthesizing and applying descriptive information. This paper provides an overview of some of the most significant contributions of science to visitor monitoring and management. It covers the related scientific purposes of explanation, causation, prediction and assessment. As scientific enquiry moves from description to evaluation, from facts to values, from providing statements of “what is” to providing statements of “what ought to be”, it ventures into more contested territory. While some advocate a substantial role for science in the establishment of normative standards about what ought to be, others believe science should be very cautious in this arena. Recreation examples, largely drawn from wilderness management in the United States, are provided.