Voters have two and sometimes three elected agents in separation of powers systems: the lower or only house, sometimes an upper house, and a president. The rules governing the election of each agent vary not only across countries, but also within them. In this chapter we look at the rules for each agent individually, describing the relative strength of the rules used to select them, and then conclude by thinking about electoral systems based on all of the choices voters make in a given country at a given time. In the next chapter we take up how the rules governing the policy-making process bring those agents, with their varying sets of preferences, together to determine policy outcomes.