If multiple discrete flaws are detected, alignment and combination rules are used to determine whether the flaws should be treated as non-aligned or as coplanar, and independent or combined flaws. Alignment and combination rules for multiple flaws are provided in Fitness-for-Service (FFS) procedures of many codes and standards in the world. However, these alignment and combination rules defined in the FFS are different. This paper aims to give overview of alignment and combination rules for multiple flaws in FFS procedures. In addition, experimental data on flat plates with parallel planar flaws are compared with the alignment rules of these FFS procedures.