A large amount of existing evidence shows that the micro- and macrostructure of feed has a strong influence on the function, development and health of the gastrointestinal tract (GIT), which, in turn, affects the performance of poultry birds. Notably, the majority of data corresponding to feed structure-induced changes in the productivity of birds has been generated from studies using broiler chickens. However, feed particle size and feed form remain an obscure and undervalued area of study in the feeding of layer chickens, with sparse evidence reported between the 1940s and 2000s. Moreover, feed in the form of crumbles and pellets, which has made a major contribution to broiler production efficiency, has not been the feed of choice for layers, where mash diets have been common practice worldwide for many years. Nonetheless, the role of feed structure in the feeding of layer chickens has recently begun to attract more interest. However, results are divergent and often not as satisfactory as expected, except in the case of gizzard weight, which typically decreases by 8% and 16% on average with finely ground and pelleted feed, respectively. The results for most performance parameters, however, are typically insignificant. In some cases where the effect of the feed form was significant, pelleting increased feed consumption by 6%, whereas a clear 9% reduction was observed in another example. The incongruities in the results are likely due to confounding factors, such as management conditions and ingredient composition of the diets. Nevertheless, the effect of feed form on the investigated parameters was more evident than the effect of feed particle size. The following review provides an overview of data from seven decades regarding the implications of feed structure on the physiology, histology, metabolism and development of the gut and the performance of egg-laying chickens.