We owe the intensive use of the terms “indexicality” and “reflexivity” to Harold Garfinkel's ethnomethodology. After being controversial when it first appeared, to the point of being compared to a cult, but then tolerated as “marginal”, ethnomethodology is now a growing response as an operational discipline of observation and reporting of professional practices. Paradoxically, this applicability is largely due to the radicalism of its epistemological position, based entirely on a careful consideration of the manufacturing operations of common sense. The purpose of this paper is to clarify this apparent paradox by showing how this “factory” works, to point the limits it imposes but also to mention the opportunities it opens, and to list some of its practical applications.