A regional magnetic map of Florida reflects the structural trends of the magnetically heterogeneous Paleozoic and Precambrian rocks underlying the coastal plain rocks. Many trends and features on the magnetic map have gravity counterparts, indicating a common source. On the basis of the regional magnetic trends, Florida is divided into two tectonic provinces with an intervening zone of intrusive rocks. Depth estimates from aeromagnetic data suggest the possibility that faulting may be a factor in the profound downwarping and accumulation of sediments in the southern province. The trends of the northern province parallel those of the Appalachian system to which they are probably related. The southern province, distinguished by northwest trends, is structurally discordant with the northern province. The magnetic evidence suggests that the southern province is a continuation of the Ouachita system which has been traced beneath the Gulf Coastal Plain to within 60 miles of the subsurface extension of the Appalachian system in Mississippi, where the two systems approach each other at nearly a right angle.