The aim of this paper is to describe Language-Neutral Syntax (LNS), a system of representation for natural language sentences that is semantically motivated and abstract, yet sufficiently concrete to mediate effectively between languages and between applications in a robust manner. LNS is semantically motivated in that it represents the logical arrangement of the parts of a sentence, independent of arbitrary, language-particular aspects of structure such as word order, inflectional morphology, function words, etc.; at the same time, LNS is not a semantic representation per se, for example using words rather than word senses as leaf nodes. We describe the basic properties of LNS structures, and show how LNS strikes a balance between abstractness and concreteness. LNS is currently implemented as the output of the NLPWin system under development at Microsoft Research, but in principle can be output by any system for any language.