A financial contract encodes the business rules that determine the generation of financial events. Its central position in the analytical methodology deserves a detailed examination. Financial contracts, when treated in a mathematical context, are often described by functions such as the fair value of an option or the present value of a bond. To understand a financial contract better, it is more useful to think directly in terms of cash flows. A financial contract is in the first place a set of rhythms, be it interest payments, rate resets or other events, which creates cash flows during the lifetime of the contract. This chapter evaluates the important rules that determine when and how financial events are generated and calculated, from which expected cash flows can be derived.