EXCITING is a state-of-the-art full-potential linearized augmented plane wave (FP-LAPW) code which uses quantum mechanics, specifically density functional theory (DFT), to determine the physical properties of solids and molecules. Augmented plane waves provide an almost ideal basis set for computing the Hamiltonian matrix for a periodic solid, and allow for tightly bound core and semi-core electrons to be treated on the same footing as valence electrons.The EXCITING code is designed so that new methods in DFT can be implemented quickly and reliably. For example, it is currently the only code available that can perform exact exchange optimized effective potential (EXX-OEP) calculations for non-collinear systems with full treatment of the core-valence interaction.EXCITING is freely available and released under the GNU General Public License.In 2009 the code has split into two branches – “exciting”, primarily developed at the University of Leoben, and “elk”, primarily developed at the Free University of Berlin and at the Max Planck Institute for Microstructure Physics.