The question that regularly arises for the engineer charged with assessing an existing structure that has not deteriorated concerns how to establish the structural diagnosis of the structure. First, it is necessary to ensure that the structure, when subjected to loads and overloads, retains its normal behavior, i.e. conforms to the design predictions. It is essential to understand why and how design and construction rules have evolved, as well as their inaccuracies, shortcomings and even errors. Reinforced Concrete from 1906 to Today details the various calculation codes introduced into French regulations, from the first in 1906 to Eurocode 2, which is currently in force.