Numeracy is the ability to use and to reason with numbers and other mathematical concepts, and to apply these in a range of everyday activities. Good numeracy appears today the best protection against unemployment, low wages and poor health. Innumeracy can then be simply defined as the absence of numeracy. That is, innumeracy refers to the growing trend in the inability of people to understand numbers, statistics, probabilities, and to being familiar with mathematical concepts. In France, the fight against innumeracy was erected as “national priority” by the law (8 July 2013). However, few empirical studies investigate the concept of innumeracy (not one to our knowledge). The program for the international assessment of adult competencies (PIAAC), which involved 7000 French participants, does only allows an indirect approach of the concept of innumeracy. Therefore, the 2011's investigation, in about 16000 households by the French national institute of statistical and economic information (Insee), seems an invaluable source of knowledge about the concept of innumeracy. This not only because the investigation included a numeracy test, but also because the participants had to understand a medical prescription (with numerical data) and were directly asked about their difficulties to read an invoice. The two main results of the present study are (1) a prevalence of innumeracy — computed on the basis of a deviation of more than 1.645 standard deviation from the mean (below it) — of about 7% in the French population, and (2) that two highly significant factors of innumeracy are level of education and gender. The understanding of a medical prescription unsurprisingly showed some supplementary difficulties in the innumeracy subgroup. However, the questioning, on a declarative basis on the difficulties to read an invoice, presumably leads to a considerable amount of avoidance strategies. The quantitative estimation of these strategies supports the idea that, for numeracy, possibly up to four times as many people show to have poor skills as those who acknowledge difficulties (Bynner & Parsons, 2006). Finally, the relation between innumeracy and dyscalculia was investigated. Dyscalculia is usually perceived as a specific learning difficulty for mathematics, or, more appropriately, arithmetic, and affects a wide range of life-long learning involving mathematics. The prevalence of dyscalculia was estimated less than 3%. This estimated prevalence is lower than the prevalence of about 5 to 7% put forward by Butterworth, Varma and Laurillard (2011). Furthermore, these dyscalculia are not necessarily real dyscalculia, but only “potential” dyscalculia (i.e., which, at least, should be corroborated by clinical investigation)