Motor Torpedo Boat (MTB) was the name given to fast torpedo boats by the Royal Navy and the Royal Canadian Navy.

The capitalised term is generally used for the Royal Navy (RN) boats and abbreviated to "MTB". During World War II the US Navy boats were usually called by their hull classification symbol of "PT" (Patrol Torpedo), and are covered under PT boat although the class type was still "motor torpedo boat".

German motor torpedo boats of World War II were called S-Boote (Schnellboote German for "fast boats") by the Kriegsmarine and E-boats by the allies. Italian MTBs of this period were known as Motoscafo Armato Silurante (MAS) which translates as "torpedo armed motorboats". French MTBs were known as Vedettes Lance Torpilles translating as "torpedo-launching fast boat". Soviet MTBs were known as Торпедный катер translating as "torpedo cutter".

After the end of World War II, a number of the Royal Navy's MTBs were stripped and the empty hulls sold for use as houseboats.

MTBs were designed for high speed, operating at night, low speed ambush (to keep noise low and to produce no wake)and manoeuvrability on the water; this was to enable them to get close enough to launch their torpedoes at enemy vessels. With next to no armour, the boats relied upon surprise and their agility at high speed to avoid being hit by gunfire from bigger ships.

A torpedo boat is a relatively small and fast naval vessel designed to carry torpedoes into battle. The first designs rammed enemy ships with explosive spar torpedoes, and later designs launched self-propelled Whitehead torpedoes. They were created to counter battleships and other large, slow and heavily armed ships by speed and agility. A number of inexpensive boats attacking en masse could overwhelm a larger ship's ability to fight them off using its large, slow-firing guns. This way an inexpensive fleet of torpedo boats could defend against much larger and more expensive fleets, albeit only in the coastal areas to which their small size and limited fuel load restricted them.

The introduction of fast torpedo boats in the late 19th century was a serious concern to navies of the era. In response, navies operating large ships introduced smaller ships to counter the threat. These were essentially similar to the torpedo boats they faced, but mounted a light gun instead of torpedoes. As these designs became more formalized they became known as "torpedo boat destroyers", and eventually evolved into the modern destroyer.