Their name says it all - AIO (all in one diapers). They work the same way as disposables do, but are reusable! Simply put on baby and bam - you're done! Everything you need is all included. They are composed of an outer waterproof shell with an inner lining of layered fabric sewn in. When the diaper is soiled, simply take it off baby and drop the whole thing in your wet bag. Simple as that. They can be purchased as sized or OS (one size). They also come in some very cute prints and deliciously plush and soft fabrics, if you can afford it!
Example of a BumGenius! AIO diaper. Click to view larger.
Pros of AIOs:
most like a disposable
simple and easy to use
good for babysitters or daycare
no effort required
Cons of AIOs:
one of the most expensive styles
can be harder to get clean
may not have enough absorbency for heavy wetters
longer drying time
I don't own any AIO diapers because they are not in our budget, but I did try one during my cloth diaper trial with Jillian's Drawers. It was extremely convenient but I personally prefer pocket diapers and AI2s!