This is a chapter from the free textbook "Economic Principles in Cell Biology" Metabolism is a dynamical process, in which a myriad of chemicals are converted via biochemical reactions inside the cell over time. This chapter motivates this dynamical nature of metabolism and introduces mathematical approaches for modelling it. Basic models of biochemical reaction rates are introduced and their assumptions and relations to each other are explained. Using these rate models, simple metabolic systems are modelled and their dynamical behavior analysed. Experimental findings on metabolic dynamics are summarised and possible explanatory models of such dynamics are discussed.