This chapter explores Quakers’ thinking about how day-to-day choices of objects and behaviours might best reflect their theology. The guiding concepts of what founding Friends spoke of as “plain” or “unostentatious,” have remained an important touchstone of Quakers’ vocabulary and identity for more than three centuries. Over time, the language, interpretations, and implications of those concepts have been reshaped by region, culture, and circumstance. With consideration to the international context of Quakerism, we examine distinctive ideas, speech, clothing, building design, and other markers of what Quakers called “outward” customs, as a way of reflecting their “inward” religious commitment.