This chapter explains briefly on networks of trade and exchange. During the transition from the Early to Middle Formative, some of the existing obsidian exchange networks broke down, others were modified, and new ones were established as new villages rose to prominence. The identification of shell materials from Early and Middle Formative Mesoamerican sites was completed by Joseph R. Morrison and the author, using the former’s extensive collections of Mesoamerican mollusks at the Smithsonian Institution. Mesoamerican obsidians occur primarily in the east-west neovolcanic chain of central Mexico and in the highlands of Guatemala. When Mesoamerican archeologists lump together commodities as obsidian, shell, magnetite, and exotic pottery as “trade items,” they may be obscuring the fact that all these items had somewhat different mechanisms of exchange, each of which needs to be understood in its own right. The chapter briefly considers two kinds of exchange reciprocity and redistribution.