Engaging and accessible, this text describes geometry as it is understood and used by contemporary mathematicians and theoretical scientists. Basically a non-Euclidean geometry book, it provides a brief, but solid, introduction to modern geometry using analytic methods. It relates geometry to familiar ideas from analytic geometry, staying firmly in the Cartesian plane and building on skills already known and extensively practiced there. It uses the principle geometric concept of congruence or geometric transformation--introducing and using the Erlanger Program explicitly throughout.