This article describes the interpretive processes historians engage in when “reading” historic buildings and examines what qualifies as historical thinking about historic buildings and sites. To gather evidence of what historical thinking looks like as it pertains to buildings, 5 practicing historians were recorded as they toured the Old North Church in Boston, Massachusetts. From these protocols, 5 heuristics were identified: origination, intertectonality, stratification, supposition, and empathetic insight. The heuristics described here provide the means through which a wider range of historic materials can be brought into the discussion of what it means to think historically.