Modern experimental and computational techniques are capable of determining bond lengths and angles with precisions of a few thousandths of an angstrom and a few tenths of a degree. Such precisions are meaningful only if they are coupled with rigorous error analysis and careful evaluation of the physical meaning of the parameters. This book demonstrates the meaning and applicability of accurate structures and their variations following a rigorous exposure of the demands and caveats in their determination. It establishes guidelines for accuracy requirements in answering broadly varying questions in current chemical research. The 21 chapters by internationally recognized authors discuss the following topics: potential energy surfaces; microwave, infrared, and liquid crystal NMR spectroscopies; gas phase electron diffraction; X-ray and neutron crystallography; electron density studies; molecular orbital methods and molecular mechanics calculations; the use of structural databases; applications to organic inorganic and organometallic chemistry; studies of reaction pathways; effects of substitution and crystal environment on molecular structure.