I will give a pedagogical introduction to Chiral Perturbation Theory (ChPT), focusing on the chiral expansion of observables for mesons. The foundations and the building blocks of the theory will be discussed extensively. In a second part, I will go over to Finite Volume Effects and Partial Quenching for ChPT, which are actual research topics I am working on. For that latter part, I will focus on the general ideas without becoming too technical, and show some example results.