Studies of how aposematism and Batesian mimicry function in nature have been made only recently. This chapter reviews the results of these studies in detail, discusses their biological significance, and calls attention to the potential of the experimental techniques for future research. The following section of this chapter is not intended to be a comprehensive review. It considers, with minimal detail, mainly those background aspects of aposematism and mimicry that are relevant to the above-mentioned studies. The cited papers, especially the reviews, provide additional information and access to the voluminous literature on these subjects. The third section of this chapter reviews some of the major studies with captive predators or at feeding stations in the field and discusses their shortcomings and some of the conclusions that can be reached from them. The remainder of this chapter is devoted to experiments with free-ranging insects in natural habitats. Hecht, M. K., Wallace, B., Prance, G. T. (eds): Plenum Publ. Corp.