First step of wheat grain transformation, i.e. milling, corresponds to successive operations of grinding and sieving which have for aim to separate the starchy endosperm (in the finest particles) from the peripheral tissues (the outer layers and germ in the largest particles). In this process, the mechanical properties of grain tissues play a role in the required energy for breaking, on the obtained particle size and on the composition of the final fractions. Direct or indirect methods were undertaken to evaluate the grain mechanical resistance and indeed allow classifying wheat samples. A hardness locus (Ha) located in the D genome of common wheat (Triticum aestivum) is known to contribute to the grain mechanical behavior and to encode two specific proteins, called puroindolines, which are suspected to play a role in the starch-protein adhesion into the starchy endosperm. Near-isogenic common wheat lines carrying or not specific mutations into puroindolines, or durum wheat into which these genes were introduced, were grown in different environments to evaluate the respective effect of this genetic hardness factor and of the environmental factors on grain mechanical property and milling behavior. Puroindoline genes were found to play a major role in the energy required to break grains, the particle size distribution and the aleurone or starchy endosperm mechanical behavior which impact the product properties. Environmental conditions were found to impact the starchy endosperm porosity (i.e. vitreousness) which can be quantified objectively and was found to introduce variations of the required breaking energy and of the particle size or the starch damaged, but do not affect the separation between the outer layers and the starchy endosperm. Experimental data also allow revisiting classical methods used to evaluate grain hardness and to identify the appropriate common wheat grain characteristics for the production of a high flour yield. Numerical modelling approaches were found to complement accordingly the experimental approach to better understand and predict the effect of changes in the wheat starchy endosperm texture on the milling behavior and thus the product properties.