Where is it permitted to flash headlights to indicate your intention to overtake?

In German traffic rules, flashing your headlights to signal your intention to overtake is allowed only outside built-up areas, both during daylight and darkness. This helps communicate your intention clearly to other drivers on less congested roads. However, inside built-up areas, flashing headlights is prohibited because it can confuse or distract other road users due to the typically closer proximity of vehicles and more complex traffic situations. So, the key rule is that headlight flashing to indicate overtaking is permitted only outside built-up areas, whether it is day or night.