Guidelines and models for procedural instructions can be supported by three types of research. Careful analytical studies of collections of instructions can help to identify, describe, and evaluate strategies that writers and designers apply. Empirical studies measure the effects of document variables on the performance of users, thus offering evidence, contraevidence, or refinements for existing guidelines. Theoretical studies, finally, aim to describe and explain the behavior of readers of instructions. To designers and writers, they provide a deeper insight in the underlying cognitive processes that determine success or failure of their work. This special issue offers research articles in all three categories.