The growing complexity of multilayer mirrors (MLMs) calls for the development of accurate and non-destructive characterization techniques suitable for routine characterization of as-deposited MLMs with sub-nm accuracy. The classical X-ray reflectivity technique shows high sensitivity to the smallest details of a multilayer structure, but the interpretation of the measured data remains complex and in some cases non-unique, even if advanced model independent data analysis algorithms are used. To reconstruct the structure of a multilayer mirror reliably a combination of X-ray reflectivity and angular dependent X-ray fluorescence data is easy to use, especially because both data sets can be measured using the same laboratory X-ray setup. The angular dependent fluorescence signal adds the information about the mean positions of distributions of individual elements and the width of their distribution. This information presents natural regularization of electron density profile that filters number of unphysical solutions that can be obtained from GIXR only data analysis. We will present the reconstruction of multilayer structures from combined X-ray reflectivity and X-ray fluorescence measurements. The strategies for optimal measurements, the value of additional data and the challenges of data analysis will be discussed.