WIEN2k is a versatile and user-friendly code for calculating the electronic structure of solids. It is based on density-functional theory (DFT) and can use a wide variety of different functionals. It utilizes the augmented plane-wave method and treats all electrons (core and valence) self-consistently, making it a very accurate method. It calculates the basic electronic structure, allows structure optimization and can simulate various spectroscopies. For X-ray absorption or electron energy-loss spectroscopy, excitonic effects can be considered using a core hole on the corresponding atom, which allows accurate simulation of various edges. It is also possible to go beyond DFT using many-body perturbation theories such as the GW approximation or the Bethe–Salpeter approach (BSE). The fully relativistic BSE method treats electron–hole interactions in a much more rigorous way and allows a proper description of the L_2,3 edges of early transition-metal compounds.