This document presents a taxonomy for classification of classroom observational data. Information for the study was accumulated in successive classes at the School of the Institute of Education, University of Helsinki and processed statistically. The taxonomy was developed through both empirical procedures and logic and concept analysis. Part one describes the purpose and function of the DPA Helsinki Taxonomy. Part two discusses the general principles behind the study, defines terminology, and describes several main taxonomical principles. Part three focuses on unit coding from several viewpoints: (a) move types (units representing verbal interaction during the instructional process), (b) cognitive content of the move; (c) social affective properties of the move, and (d) modes of teacher influence. Part four discusses periodic coding (i.e., coding of sequences of instructional situations devoted to the same task) in terms of division of labor and responsibility in the classroom, formal characteristics of verbal communication, and goal-related behavior. Part five offers reliability data. (A list of references is included.) (JS)