This unit introduces students to the foundations of geometry through constructions and rigid transformations. Students explore geometric properties without relying on measurements, using constructions to develop conjectures, justify reasoning, and deepen their understanding of shapes and relationships in the plane. Building on their prior experiences with transformations, students learn to create and analyze rotations, reflections, and translations using geometric tools rather than coordinate grids, leading to more formal and rigorous definitions. Throughout the unit, students develop mathematical argumentation skills, use a geometry reference chart to support formal reasoning, and select appropriate tools, including traditional geometry instruments and dynamic geometry software, to investigate and communicate mathematical ideas.