[en] The electronic structure of molecules is discussed and the techniques of electronic structure calculations presented. Without exception the molecular electronic wave functions are expanded in some convenient, but physically motivated set of one-electron functions. Since the computational effort strongly depends on the number of expansion functions, the set of functions must be limited as far as possible without adversely affecting the accuracy of the wave functions. The choice of such functions is discussed for molecular calculations. Some particular molecules including hydrogen are considered. 28 references