Before making your purchase, find out what type of speakers you will be replacing. You can simply measure the existing speakers and go from there. If you do not have any to begin with, a local Audio/Video shop can guide you with a few simple questions about your vehicle. Most of the time you will be able to drop them right in with little to no alterations needed. Pay close attention to the RMS power handling of the speakers you are purchasing. This is the continuous power that a speaker can handle without distorting. Your head unit will have to have the proper number of speaker outputs compared to how many speakers you plan to hook up to it, as well as sufficient power from the built-in amplifier. Sometimes though, a separate or external amplifier will have to be employed so that your speakers get the adequate power they need for optimal performance.