This introductory paper to the compendium on the South Bay Middle Period provides a brief discussion of the organization and prominent themes of the papers. Organized primarily by the age of the sites discussed, the papers present a wide variation in the archeological record for the Middle Period. Variation in settlement patterns, artifact types, and cemetery data is brought out in the studies. Through the myriad of variation, recurrent trends during the Middle Period are seen. Times of inundation evidently caused widespread settlement relocation among prehistoric populations in the South Bay. Also, a possible intrusion of Windmiller culture is noted particularly in the record of the southeastern portion of the Bay Area. These and other patterns in South Bay archeology serve to better illuminate the local Middle Period while also exposing ill-understood areas for needed research.