XCrySDen is a crystalline and molecular structure visualisation program aiming at display of isosurfaces and contours, which can be superimposed on crystalline structures and interactively rotated and manipulated. It runs on GNU/Linux. XCrySDen has been also ported to Mac OS (requires X11) and Windows (requires either CYGWIN or WSL). The name of the program stands for Crystalline Structures and De