Housings are the plastic backing which your lenses mount to and your bulb socket attaches to. On most modern vehicles the lenses are chemically cemented to the housings. This means that if you wish to try to reuse your OEM housings, you will have to use a dremel or bandsaw, and files to physcially chop the amber lens from the factory housings, file them down and then epoxy the new lens in its place. If you are handy with these tools and have the time, it can be done. In most cases though, it is far easier to just order the housings as well. This way you will recieve an assembled, ready to install set.