Presidential and parliamentary systems differ mainly in their structure and operation. In a **presidential system**, the president is both the head of state and government, elected separately from the legislative body. This promotes a clear separation of powers but can lead to gridlock. In contrast, a **parliamentary system** merges the executive with the legislative; the head of government (usually a prime minister) is drawn from the legislature, promoting cooperation but potentially leading to less stability if coalition governments fail. Each system reflects distinct **governance dynamics**.