Following a review of the basic ingredients necessary for constructing models of galactic chemical evolution, with a special emphasis on the issue of stellar evolution and nucleosynthesis (which is treated in detail in Chapter 2), I continue with the basic equations that one needs to solve in order to follow the chemical evolution of a system of gas and stars in time and space. The assumptions of the models I have handled with the aim of addressing different aspects of the formation and evolution of the Milky Way and elliptical galaxies are discussed in Chapter 3. In Chapters 4 and 5, I present the results of my own research, mainly focusing on how important is the analysis of the chemical abundances and especially abundance ratios in galaxies for understanding their formation and evolution, in spite of the many parameters involved in the modelling.