The solid-state structure of unsolvated, Lewis base-free phenyllithium (LiC6H5) is reported. Structure determination of the simplest lithium aryl was performed by high-resolution synchrotron X-ray powder diffraction. The structure was solved by ab initio methods in combination with difference Fourier analysis and consecutive Rietveld refinements. Solid phenyllithium consists of dimeric Li2Ph2 molecules, which strongly interact with adjacent Li2Ph2 moieties, forming a polymeric, infinite-ladder structure along the crystallographic b-axis. In the Li2Ph2 units the two lithium atoms and the C(ipso) atoms of the two phenyl rings form an absolutely planar, four-membered ring with the two phenyl rings perpendicular to it. The bonding of the C(ipso) atom to the two Li atoms can be described as a three-center, two-electron bond (Li-C 2.24(1) and 2.32(1) Angstrom; Li-C-Li' 63.2(7)degrees). The pi-electrons of the phenyl rings interact strongly with the lithium atoms of neighboring Li2Ph2 moieties.