Trailer

Any vehicle designed to be towed by another vehicle is classified as a trailer. A bicycle trailer used to transport children also falls under the category of trailers.
A passenger car or van can also be towed. The driver of the passenger car or van must have a valid driver’s license.
There are rules for towing trailers behind cars. If a car is towing another car, the driver of the towed car must have a valid driver’s license. Passengers must also be seated in the towing vehicle as much as possible.

Suppose you hold a car driving license, category B. In that case, you are always permitted to transport a trailer with a maximum permissible weight of 750 kilograms, even if the weight of the car plus the trailer exceeds 3500 kilograms.

Article 1a. of the RVV: Trailers: Vehicles that are propelled by a vehicle or are clearly intended to be propelled in this way, as well as semi-trailers.