My fridge is leaking onto the floor: 

 Frost free fridge.

There are several things to check for. The condensing defrost tray under the fridge can crack or develop a hole and leak onto the floor. A door gasket not closing properly may cause sweating and leak onto the floor. Some fridge's have a humidity switch inside the fridge that should be turned on to prevent sweating on the center bar between the fridge and freezer section. If your fridge has developed a frost free failure problem, often the frost will travel down the suction line at the back of the fridge and drip water on the floor. The heat exchanger tubing can separate and also sweat and drip on the floor. A kit to repair a separated heat exchanger line, comes with instructions as well. Ice maker and chilled water fill lines can crack and leak as well, this is fairly common with the plastic lines as they can dry out and crack.

Self defrosting fridge.

If the water is comming out the front, The the drain tube under the evaporator is blocked. 

In tke back of the fridge under the evaporator is a channel. This is connected to the drain tube that run down to the drain pan on the compressor. The heat from the compressor will evaporate the water.

Blow this tube open with compressed air or use a pice of wire to open it.

If you find that the tube is in fact frozen up, it must be rerouted. On older fridges the foam around the tube get wet, this will freeze and that will freeze the drainwater in the tube. 

If the water is comming from the  back, the drain pan is leaking or the drain tube is not dripping into the pan.

The pan can be replaced by a cheap aluminiun pie pan, stuck on with a bit of silicon.