A parliamentary system differs from a presidential system primarily in the relationship between the executive and legislative branches. In a parliamentary system, the executive branch derives its legitimacy from the legislature and is directly accountable to it, often leading to a closer alignment between the two. Conversely, in a presidential system, the president is elected independently of the legislature, which can create checks and balances but may also result in gridlock. These structural differences influence governance styles, policy-making processes, and the overall political dynamics in a country.