In a perfect world, your yard would be graded so that all the run-off from rain diverts around your home and off into never-never land where it will never bother you again. Unfortunately, this is a real fairytale for some home owners that get stuck with a built-in swimming pool they never counted on, and end up have a yard drainage problem.
If there is an area of your yard that is lower that the soggy bottomed backyard, then the yard drainage problem solution can be to install what is known as a "curtain drain." This is simply a trench that is dug from the wettest area of your yard to a lower spot. It doesn't have to be deep (12" - 18" deep is perfect) but it does have to slope downward to that lower area. Once it is dug, you would add 2 or three inches of gravel stone into the bottom and then lay a perforated pipe on top. PVC is the best material to use for this as it doesn't crush like the flexible black plastic pipe that landscapers like to use.
Once you have the PVC pipe in place, cover it with more gravel until it is completely buried. Then add a layer of weed barrier (a burlap like cloth that will stop the soil from clogging the pipe) and fill the hole back in with soil. Finally, you can seed or sod the surface. Once complete, the curtain drain will be completely invisible. Rain will flow to the low spot, fall into the trench, and then be redirected to the lower yard where it can drain out to the surface or seep back into the soil, bringing an end to your yard drainage problem.