Second Lieutenant is the lowest commissioned rank in many armed forces.

In the United States Army, the rank bore no insignia until 1917 when a gold bar was introduced to contrast with the silver bar of a First Lieutenant. As a result those in the rank have often been referred to as "Butterbars". The rank is also used in the United States Air Force and the United States Marine Corps. The corresponding United States Navy rank is Ensign.

The rank was introduced throughout the British Army in 1871 to replace the rank of Ensign (Cornet in the cavalry), although it had long been used in the Royal Artillery, Royal Engineers and Fusilier regiments. At first the rank bore no distinct insignia. In 1902 a single star (sometimes referred to as a pip) was introduced; the ranks of Lieutenant and Captain had their number of stars increased by one to (respectively) two and three. The rank is also used by the Royal Marines.

In the Royal Air Force the comparable rank is Pilot Officer. The Royal Navy has no exactly equivalent rank, and a Second Lieutenant is senior to a Royal Navy Midshipman but junior to a Sub-Lieutenant. New Zealand's navy - breaking with Royal Navy tradition - uses the Ensign grade for this rank equivalent.

In Germany the rank is Leutnant.

See also

• Comparative military ranks
• US Army officer rank insignia
• British Army officer rank insignia