According to France’s National Literacy Agency (Agence Nationale de Lutte Contre l’Illettrisme: ANLCI), “functional illiteracy describes the situation of people aged over 16 who, despite having attended school, are incapable of reading and understanding a text that concerns situations in their everyday life, and/or are unable to convey simple information in writing.” Functional illiteracy (illettrisme) is distinct from illiteracy in the strict sense (analphabétisme), which concerns adults who have had inadequate schooling or none at all. Experts distinguish two specific skills involved in reading: (1) “reading” a word by means of “recognition”, “identification” or “decipherment”, and (2) understanding a text. Following up on studies by Emilia Ferreiro and others, we have developed an approach to assess adult illiteracy called “Diagnosis of modes of appropriation of written texts” (Diagnostic des Modes d’Appropriation de l’Écrit: DMA) (Besse et al., 2004). In one-on-one interviews, modelled on psychological consultations, we measure abilities to read, write, speak, understand a spoken text, a written document, and so on; but we also examine how respondents relate to the protocol applied, and how the protocol influences the results gathered. The ANLCI module of the 2004 IVQ Survey comprises three types of tests: writing a text; identification of words and pseudo-words; reading comprehension. The data-gathering procedures are designed to create a reassuring setting for respondents that will induce them to perform the proposed tasks. The number of “non-responses” (“I don’t know”, refusal to respond, and lack of response) turned out to be small, despite the known reluctance of the categories concerned to undergo any form of assessment. Apparently, the choice of situations, the order in which tests were administered, and the role of the “orientation module” in reassuring respondents all helped to achieve the Survey’s objectives.