We review here the scant evidence pertaining to the early arrival of people in Southeast Mesoamerica and what is presently known about the timing and nature of the first efforts to domesticate plants in the area. Most of the chapter summarizes the different forms that sociopolitical complexity took in the Southeast during 1600–400 BCE. It was during this period that the first monumental platforms were raised in the area, suggesting the emergence of leaders who could plan these projects and command the labor to complete them. While such constructions speak to a modicum of political centralization, they did not necessarily signify the existence of hierarchies. People in different areas thus used similar things, such as large buildings, to craft different, locally specific power relations. Such variety sets the stage for the different political histories that will take shape in the coming centuries.