Current understandings of the archaeology of second-millennium B.C.E. central western Anatolia are enriched by ongoing research at Kaymakçı, located in the Marmara Lake basin of the middle Gediz River valley in western Turkey. Discovered during regional survey in 2001, the site offers a critical node of exploration for understanding a previously unexamined period in a well-traversed geography thought to be the core of the Late Bronze Age Seha River Land known from Hittite texts. Here we present results from the first three seasons of excavation on the citadel of Kaymakçı plus a study season (2014-2017), introducing the site's chronology, historical and regional context, and significance through presentation of excavation areas as well as material and subsistence economies. With reference to such evidence, we discuss the site's development, organization, and interregional interactions, demonstrating its place in local and regional networks that connected Aegean and central Anatolian spheres of interest. 1 christopher h. roosevelt et al. 646 [aja 122 introduction The Kaymakçı Archaeological Project (KAP) was established in 2013 to conduct excavations and related activities at Kaymakçı, a second-millennium B.C.E. site located in the Marmara Lake basin of the Gediz River valley, province of Manisa, western Turkey. 2 Building on the preliminary results of the diachronic Central Lydia Archaeological Survey (CLAS, 2005-2014), 3 excavations at Kaymakçı began in 2014 with the aim of exploring the development, spatial organization, and economies of the site. With four seasons of research now complete including the 2017 season, 4 this article focuses on the implications of results from excavations and material analyses for understanding activities and interactions across the site, the region, and the broader Aegean and Anatolian worlds during the second millennium B.C.E. Excavations at Kaymakçı are planned to continue at least six more years, according to the 10-year research program submitted to the Turkish Ministry of Culture and Tourism. Final publication of excavation sectors and finds will follow, while separate articles will treat specific sets of data. regional setting and previous research Kaymakçı is situated above and along the western shore of Lake Marmara, an approximately 50 km 2 inland lake located along the northern margin of the Gediz (classical Hermus) River valley, about 100 km 2 We thank P.J. Cobb, T. Kaner, and E. Moss for their essential implementation and management of the recording system in the 2014-2016 field seasons. We give thanks also to all project participants between 2014 and 2017, including K.