Robert Jackson's tenth and most ambitious book explores the factors and dispels the false ideas around how the fringes of Spain's empire in the Americas developed. He details how environmental differences and socio-cultural variations had a controlling influence on development of the missions in each region and how these factors explain the striking differences in the mission structure.

Jackson's extensive on-site research covers New Mexico (1598-1580 and 1696-1833), the Rio de la Plata region (1609-1848), the Primeria Alta Region (1687-1833), Texas (1690-1695 and 1716-1815), Baja California (1697-1833), and Alta California (1769-1833).

Missions and the Frontiers of Spanish America is a readable and generously illustrated book that puts the role of the missions, missionaries, and indigenous peoples into a broader historical context.