Starting at an introductory level, this work leads to important and often new results in synthetic differential geometry. From rudimentary analysis the book moves to such results as: a new proof of De Rham's theorem; the synthetic view of global action, going as far as the Weil characteristic homomorphism; the systematic account of structured Lie objects, such as Riemannian, symplectic, or Poisson Lie objects; the view of global Lie algebras as Lie algebras of a Lie group in the synthetic sense; and, lastly, the synthetic construction of symplectic structure on the cotangent bundle in general. Thus, while the book is limited to a naive point of view developing synthetic differential geometry as a theory in itself, the author nevertheless treats somewhat advanced topics, which are classic in classical differential geometry but new in the synthetic context.