One-dimensional population balances are used as a modelling tool for a variety of chemical processes. In particle technology population balances are typically used for modelling agglomeration processes – e.g. in fluid bed granulation processes. In this text the population balances are introduced and fully derived with focus on each of the terms in the balance. The text is an excellent starting point for beginners and thus you will be familiar with the basic principles and theory within this relevant chemical engineering field on a bachelor or master-of-science level.