This chapter on Interactional Ethnography (IE) lays out the guiding logic-of-inquiry and the governing principles of operation and conduct (Heath, 1982), and the theoretical perspectives guiding the iterative, recursive and abductive (IRA) logic and actions (Agar, 2006) that constitute Interactional Ethnography (IE) as a logic-of-inquiry. This logic-of-inquiry guides outsiders (ethnographers) as they seek to develop understandings of what insiders need to know, understand, produce and predict as they learn with, and from, others in particular educational and social environments (Heath, 1982; Street, 1993). Specifically, an IE logic-of-inquiry supports researchers in exploring what is being constructed in and through micro moments of discourse-in-use, historical roots of observed phenomena, and macro level sources that support and/or constrain the opportunities for learning afforded to, constructed by, and taken up (or not), by participants in purposefully designed educational programs (e.g., Castanheira, Crawford, Green & Dixon, 2000; Green, Skukauskaite, Dixon & Cordóva, 2007; Bridges, Botelho, Green & Chau, 2012). This goal, as we will demonstrate complements the goals of the learning scientists who seek to develop situated understandings of learning as a social and cognitive construction (Danish & Gresalfi, this volume), and a design-based research approach (Puntambekar, this volume).