This article is intended as a kind of precursor to the document Geometry for Post-primary School Mathematics, which forms Section B, pp. 37–84 of the Mathematics Syllabus for Junior Certicate issued by the National Council for Curriculum and Assessment [16] in the context of Project Maths. Our purpose is to place that document in the context of an overview of plane geometry, touching on several important pedagogical and historical aspects, in the hope that this will prove useful for teachers. The main points we want to emphasize are these: • Geometry is a key part of mathematics. • Children must pass through different stages in studying geometry. • Each stage plays an important rôle. • Care must be taken in managing the transitions. • Some knowledge of history is useful for teachers.