In 2001 Razumov and Stroganov conjectured that the (properly normalized) components of the ground state of the dense O(1) loop model on a semi-infinite cylinder enumerate fully-packed loop (FPL) configurations on the square, with alternating boundary conditions, refined according to the link pattern for the boundary points. This conjecture has arisen a lot of interest both in the physics and in the mathematics community. \par In this talk, after reviewing the main background, I will present a proof of this conjecture. The main idea is to recognize the fundamental role of ``gyration'', an operation that can be performed on FPL, which was already the key in Wieland's proof of the rotational symmetry of the FPL enumerations.