At one time, dog crates were a fairly simple matter. They were your basic
cage with a door. That's not how it is any longer, though. Dog crates have come a long way during the last couple of decades. Today there are new designs, new materials, new safety devices, and a host of other improvements to make your dog more comfortable and to add to your sense of well-being and security.
Today's dog crates can be used for house
training, as a play pen, for security
, or for traveling.
In general, there are two broad types of dog crates. The first are those that you set up and (more or less) leave in place, and the second type is the newer fold and carry kind. The fold and carry type is by far the most popular, because of its ease of use and mobility. These types can be taken practically anywhere and set up in minutes. Dog owners are no longer bound by the restrictions of having to leave their dog at home because they have no place to put him.
When you are shopping for a dog crate, make sure you consider a few details before buying:
The most important detail is size. You will want a dog crate that is a little larger than what is recommended. Your dog will not be happy if he's stuffed into a crate that is too small. He won't be able to move freely and, in fact, he may suffer because of it. Getting a size that is a bit larger than what you think he needs is a good idea, and will pay off later with added happiness on your dog's part.
If you're going to take your dog crate with you on road trips, it is highly recommended you consider the fold and carry type. They are easy to set up and they don't take up much room in the car or truck. These, too, come in various sizes, so pick one that offers the most space for your pet.
Take a good look at the door security device. Most people like the drop pin type. It's easy to use and very effective in keeping the door closed. If you opt for another type, make sure it's one that you can open and close easily.
If you plan to fly with your dog, make sure the dog crate you purchase is approved for airline use. 
The International and Domestic Air Transport Association sets the guidelines on dog crates approved for flight. If your dog crate is approved, it should say so. If it doesn't, you may want to check further to ensure that it is. You do not want to show up at the airport only to be turned away because your crate is not appropriate.
Lastly, there are new types of dog crates that are actually soft. They are called dog dens and, like the fold and carry type, they are completely portable and very comfortable for your dog. These dog crates are used primarily for commuting, and while they are comfortable and easy to use, they may not be what you need for regular backyard purposes.
