This special issue works toward refining the understanding of a construct that has had a name for nearly 30 years and has been used by educators of all stripes for centuries. The introduction lays the groundwork for discussing the issues addressed throughout. Each of the papers address different aspects of a similar problem: How can we conceptualize, design, and assess the effects of scaffolding when it is implemented in a complex classroom system? The first article addresses a core problem in conceptualizing scaffolding: What are the specific goals of scaffolding provided in software tools? The next paper extends this consideration of how scaffolding mechanisms can complement each other and explores issues having to do with the complex settings in which scaffolding is used. A framework which synthesizes theoretical and design work done in cognitive science, psychology, educational technology, science education, and the learning sciences over the last three decades is the topic of the third paper. The final article presents a new method for analyzing the effects of scaffolding. This special issues closes with commentary covering different components of a definition of scaffolding, including the "what, why, and how" of scaffolding.