Virginia and Tennessee had jointly surveyed and settled their shared boundary without formal congressional approval. Virginia later challenged the boundary as unenforceable for lack of consent under the Compact Clause. Justice Field's opinion drew a distinction that still governs: consent is required only for compacts that would encroach on federal power or the political balance among states. Ordinary boundary settlements, reciprocal enforcement agreements, and interstate cooperation on matters of purely local concern do not. Virginia v. Tennessee is the reason the modern web of interstate compacts — from the Port Authority to driver's-license reciprocity — can operate without a floor vote in Congress for every arrangement.