jackal24

Some large AC have fuel dump systems, some don't. If you are in a airplane that doesn't have one, you have 2 choices:
1. Burn off the fuel until below max landing weight.
2. Land overweight.

The choice depends on the emergency. For example, if you are on fire, you are not going to wait to land. The airframes are designed to land at these weights, just not on a normal basis and inspections need to be completed after an overweight landing is performed.

sailingfun

It depends on the aircraft. Many do not have any way to dump fuel. If a aircraft can't dump then it must be able to make a safe landing at the max certified takeoff weight. The decision to land ASAP or burn down fuel depends on the nature of the emergency. The pilot in command has to decide if landing ASAP is safer then holding to burn off fuel. Every situation and decision is unique however if the airworthiness of the aircraft is in question its generally best to get it on the ground even if it means possible brake and truck damage in a overweight landing due to brake energy absorbed and the follow on heat buildup.
As a side note even aircraft with fuel jettison ability often have to make overweight landings. In the 767ER as a example you can only dump center tank fuel not the wings and the dump rate with the now required fuel pump AD is only about 1300 pounds a minute.