Research results are collated and presented concerning the change in Finland from a binary system of education to a more unitary system, the "comprehensive school," involving a single primary school (grades one through nine) and a choice between vocational and senior secondary school (grades ten through twelve). The new system, being implemented on a nationwide basis, is described in relation to that existing previously, and research results are presented concerning (1) the conception and development of the "comprehensive school" idea, (2) progress toward equality of educational opportunity, (3) grouping procedures and their flexibility, (4) academic achievement of pupils, (5) affective achievement of pupils, and (6) new, system-centered problems. Advantages and disadvantages of"comprehensive education" as revealed in the research are discussed, and an outline of the decision-making process for research conduct and finance is presented. Thirty-nine studies are cited in the reference list, and a glossary of terms unique to the "comprehensive system" is presented. (MB)