The scaffolding metaphor was originally developed to describe the support given by a more expert individual in a one-on-one interaction. Since then the notion of scaffolding has been applied more broadly, and it has been transformed and generalized. Most recently, it has been used by researchers in the learning sciences to describe features and functions of technological artifacts, especially those of educational software. In this article, we present an analytic framework that we believe can guide and systematize these new uses of the scaffolding metaphor. In this new framework, 'scaffolds' are not features of artifacts or situations, nor is 'scaffolding' something that may be occurring (or not) in a given situation that we observe. Rather, a scaffolding analysis is a kind of comparative analysis that we perform on learning interactions. Because this analysis is comparative, it always produces results that are relative to specific choices that we make in framing the comparative analysis. This article presents a theoretical argument for our proposed framework, and illustrates the definition by applying it to two software environments. (Bruce Sherin, Brian J. Reiser, and Daniel Edelson)