List of current state leaders by date of assumption of office

This is a list of current state leaders ordered by their continuous tenure in a position of national leadership. For countries in which the head of state and head of government are separate, both offices are listed. For leaders who held the same office prior to their state's independence, the start of their tenure is used, not independence. For a list of heads of state taking dates of independence into account, see List of heads of state by diplomatic precedence.

Acting presidents are included in this list, but if a leader has non-consecutive terms, only the current period of service is listed.

States where head of state differs from head of government are mainly parliamentary systems. Often a leader holds both positions in presidential systems or dictatorships. Some states have semi-presidential systems where the head of government role is fulfilled by both the listed head of government and the head of state.