Belgium
In Belgium, weapons that launch a projectile without the use of a combustion/fire are unrestricted. This includes those used for Airsoft and Paintball. However if a weapon is shorter than 60 cm, or has a barrel shorter than 30 cm and shoots with more than 7.5 joules of energy (measured 2.5 meters from the muzzle) it is classified as a firearm and needs registration.
In general, all events must take place in private locations. Organizations may host airsoft events under the condition that they are not affiliated with ideological or religious agendas.
There is no clear law on how to transport airsoft replicas, but it is commonly accepted among players to transport your replicas as if they were real firearms, as to avoid any chance of hassle with the authorities. This means that the replicas must be covered while transporting them through public domain, in a gun-bag for example.
The use of gun-mounted lasers or night-vision scopes/sights is illegal for civilians, however the use of regular scopes/sights (even illuminated ones) and night-vision -goggles- isn't. This is because gun-mounted lasers and night-vision scopes/sights are looked upon as being only useful in military context or for assassination (which is, of course, illegal).
Read more about this topic: Legal Issues In Airsoft