The book is devoted to the problem of evolution of densities in dynamical systems described by delay differential equations. ... The book is interesting and introduces the reader to the problem of the evolution of the densities. Indeed, formulating (if possible) such an evolution one is able to guess the asymptotic behavior of the solutions with known density of their initial values. The examples in the book are carefully selected in order to illustrate the main theoretical results. (George Karakostas, zbMATH 1462.37001, 2021)