The theory of complex variables is significant in pure mathematics, and the basis for important applications in applied mathematics (e.g. Fluids). This text provides an introduction to the ideas that are met at university: complex functions, differentiability, integration theorems, with applications to real integrals. Applications of applied mathematics are omitted, although Fourier transforms is mentioned. The first part is based on an introductory lecture course, and the second expands on the methods used for the evaluation of real integrals. Numerous worked examples are provided throughout.