GISAXS stands for Grazing-Incidence Small-Angle X-ray scattering and is a scattering technique most commonly done at synchrotron radiation facilities. A related technique also exists for neutron scattering (GISANS). GISAXS is a powerful tool to study nanostructured surfaces and thin films, combining the accessible length scales of small-angle x-ray scattering (SAXS) and the surface sensitivity of grazing-incidence diffraction (GID). Application range from the characterization of quantum dot arrays and growth instabilities formed during in-situ growth, as well as self-organized nanostructures in thin films of block copolymers, silica mesophases, and nanoparticles.

As a hybrid technique, GISAXS combines concepts from transmission SAXS and from GID. From SAXS it uses the form factors and structure factors. From GID it uses the scattering geometry close to the critical angles of substrate and film, and the two-dimensional character of the scattering, giving rise to diffuse rods of scattering intensity perpendicular to the surface. GISAXS also shares elements of the scattering technique of diffuse reflectivity such as the Yoneda/Vinyard peak at the critical angle of the sample, and the scattering theory, the so-called distorted wave Born approximation (DWBA). However, while diffuse reflectivity remains confined to the incident plane (the plane given by the incident beam and the surface normal), GISAXS explores the whole scattering from the surface in all directions, typically utilizing an area detector. Thus GISAXS gains access to a wider range of lateral structures and, in particular, is sensitive to the morphology and preferential alignment of nanoscale objects at the surface or inside the thin film.

<ref>http://staff.chess.cornell.edu/~smilgies/gisaxs/GISAXS.php</ref>
<ref>http://www.gisaxs.de/index.html</ref>
<ref>http://www.insp.jussieu.fr/axe2/Oxydes/IsGISAXS/isgisaxs.htm</ref>