Reasons for the C-13 NMR gamma-gauche effect in sulfoxides, i.e., the distinct shielding of a carbon beta to a gauche-oriented sulfoxide group were investigated. Several calculated and measured C-13 NMR data of open chain or thiane-derived sulfoxides revealed that an upfield shift is only observed for that gamma-gauche position, in which the respective carbon is anti to the sulfoxide's sulfur lone pair. Carbons in gamma-gauche position, which are synclinal to the lone pair, are not affected. The magnetic anisotropy of the S=O group was examined by generation of iso-chemical-shielding surfaces (ICSSs) and magnetically induced current maps. Stereoelectronic interactions were determined with natural bond orbital (NBO) and natural chemical shielding (NCS) analyses. The gamma-gauche effect is best described by stereoelectronic interactions, especially those of the sulfur's lone pair with antibonding orbitals to a beta-carbon in antiperiplanar orientation. An explanation based on steric interactions, which has frequently been referred to, is not suitable to describe the observed shielding effects. Furthermore, a description of the bonding situation in the S=O group is given. It can be understood as S-O triple bond, where the bond order is significantly reduced by antibonding contributions in some of the occupied molecular orbitals.