One of the most fundamental things a budding racing driver must learn is what the various flag signals used around the track mean.

Motor Racing flags are used to indicate track conditions and to communicate important messages to drivers. 

Typically, the starter waves the flags atop a flag stand near the start/finish line and track marshals are stationed at observation posts around the circuit in order to communicate to the drivers.

Yellow flag - danger

The yellow flag indicates a hazard ahead, such as a stranded car. A single waved yellow flag warns drivers to slow down as there is a hazard ahead. Two waved yellow flags at the same post means that drivers must slow down and be prepared to stop if necessary. Overtaking is prohibited until the hazard is cleared, or the next marshals post shows the green flag.

 

Green flag - all clear

The green flag is waved at the back of the grid when all the cars are ready in their designated grid positions and that it is all clear to commence the start procedure. Out on the track it is shown when a driver has passed the potential danger point and the yellow flags have been lifted. 

 

Red flag - stop

Most importantly, the red flag indicates that the session has been stopped, usually due to poor track conditions, an accident, or that the track is blocked.

 

Blue flag - car behind trying to overtake

The blue flag, when shown to a driver, indicates that a faster car is behind trying to overtake. It is also shown to warn a driver that they are about to be lapped and must give way to the lapping driver or drivers. If the driver being lapped should pass three blue flags being displayed consecutively, then that driver risks being penalised.

 

Yellow and red striped flag - danger, slippery track surface

The yellow and red flag warns drivers of a slippery track surface, usually due to oil or water. 

 

Black with orange circle flag - mechanical problem

Accompanied by a car number, this flag warns a driver that he has a mechanical problem and must return to his pit. For example a car’s bodywork may be damaged and has the dangerous potential to fly off and hit another car.

 

Half black, half white flag - unsporting behaviour

Accompanied by a car number, this flag warns of unsporting behaviour. This may be followed by a black flag if the driver does not heed the warning.

 

Black flag - driver to return to the pit

This is the naughty boys, or girls, flag! When accompanied by a car number, it directs the driver to return to their pit and is often used to signal to the driver that they have been excluded from the race. 

 

White flag - slow vehicle on track

The white flag warns of a slow moving vehicle on the track, whilst in American racing it signifies the last lap.

And finally, the flag most drivers want to see:

 

The Chequered flag - finish

The chequered flag indicates to drivers that the session has ended. During practice and qualifying sessions it is waved at the allotted time, whilst during the race it is shown first to the winner, and then to every car that crosses the line after the winner.