A V5 is a term that can refer to two different things:

1. A V5 engine is a five-cylinder piston engine where the cylinders share a common crankshaft and are arranged in a V configuration. V5 engine designs are very uncommon, with the first production version of one being the 1997–2007 Volkswagen Group VR5 engine.

2. A V5 logbook, also known as a V5C, is a document that registers a vehicle with the Driver and Vehicle Licensing Agency (DVLA) in the UK. It records the registered keeper(s) of the vehicle, which is the person or business registering and taxing the vehicle, not necessarily the owner. The logbook contains essential information about the vehicle, such as the date it was first registered, its manufacturer, and the colour and engine size. It is illegal to drive a car without a V5 logbook, and it is strongly advised not to buy a car without one as it carries a risk of being stolen, written off, or having finance owed on it.