The power of the combined application of quantitative low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) is demonstrated for several examples. It is shown that the STM image in most cases provides the key to the applicable structural model type. Such an initial guess is needed by LEED to start a structural search in which the model parameters are varied so that the complete crystallographic structure is obtained. The input from STM is invaluable when a large number of different model types have to be tested or, even more, in cases where the scientist lacks the imagination to think of the correct model type. If a structural misinterpretation of the STM image puts LEED on the wrong track, then the method becomes aware of that by the best fit achieved being unsatisfying. In this sense, the combination of STM and quantitative LEED is almost ideal and provides new power for the access of complex structures.