Call it Car Stereos, Radios, or In-Dash Receivers, the facts remain, the head unit is one of the most important parts of a car audio system, and when it comes to choosing one, your truths is ample. Before you fall in love with the best Alpine, Kenwood, Clarion and or Pioneer has to offer be aware that the units come in three different sizes. These sizes consist of DIM (about 2 inches in height), DIM and a half (3 inches in height), and that now popular double DIM (4 inches in height). Furthermore, it is also important that you take into consideration any plans you may have for your car audio system. If you are not planning to amplify your system a high-power unit is the most desired. However, if you are going to use amplifiers in your system other options such as front and rear sub and center RCA's are best suited. Also before buying a Car Stereo Receiver is always a good idea to take a look at the reviews. See where people who own your desired model and brand are saying before you make an investment.