In the Shadow of Titans
Based on what little evidence we have it seems that all jotuns are organized in familial clans lead by a chieftain called a jarl, and with all clans sharing the same descent keeping amongst themselves. Each of these clans is largely autonomous, but all swear fealty to their high king, who is generally elected amongst each of the jarls. Three broad social classes generally exist in giant society. Thralls consist of slaves and bondsmen, karls which are what the majority of giant society consists of, and jarls, which are the aristocracy. The boundaries between classes are generally a lot looser than amongst their human counterparts, but it should be noted, that this idea of looseness only applies to fellow giants. non giants are never allowed to rise up above the position of a thrall. It should be noted that different giant races generally keep to themselves and their own clans, but as stated previously all swear fealty to the one high king.
The current high king is Gunnvald Odinsonn.