This article briefly reviews fundamentals of single-crystal X-ray diffraction and describes two extensions of standard X-ray diffraction studies: kappa refinement and multipole refinement. Standard single-crystal X-ray diffraction study is based on the conventional refinement technique which yields positions and thermal displacement parameters of the atoms in the crystal. In addition, kappa refinement gives information about net atomic charges. Multipole refinement, besides giving information similar to kappa refinement, describes non-spherical charge density distribution around atom nuclei and hence makes it possible to visualise bonding features, such as covalent bonds and lone-pair orbitals. Elements and further possibilities of modern charge density studies are summarised.