C*-algebras are algebras of bounded operators on Hilbert space, which were introduced to study quantum mechanics. Many types of C*-algebras are created from a certain object called C*- correspondence, which is a bimodule over C*-algebras. I will introduce two categories constructed by using C*-algebras and C*-correspondences. We will see that many important questions in C*-correspondence theory can be answered by investigating these questions in a categorical setting.