The difference between a parliamentary and a presidential system of governance lies in how executive power is structured. In a parliamentary system, the executive branch derives its legitimacy from the legislature and is often led by a prime minister, who is accountable to parliament. Conversely, in a presidential system, the president is independently elected, holding significant powers separate from the legislature. Each system affects how policies are formulated and implemented, with parliamentary systems promoting collaboration while presidential systems often encourage distinct separations of power.