Most hearing aids are custom molded and individually fit to each ear. Many factors such as degree of hearing loss, dexterity, and cosmetics will determine the style or model that is best for you. Most circuits can be built into a variety of models.

CIC - Completely-In-the-Canal The CIC is the smallest model. It is cosmetically attractive with good sound quality and works best on mild to moderate hearing losses. Not all ears can be fitted with CIC hearing aids due to size limitations.
ITC - In-The-Canal The ITC size is the smallest model which can accomodate directional microphones. This size allows more venting for comfort and uses a longer life battery than the smaller CIC. The Half Shell model is a slightly larger version of the ITC.
ITE - In-the Ear The ITE style is custom fitted using the entire bowl of the ear. This larger size makes the aid easier to handle for users with dexterity problems. They can be made more powerful than other custom styles to fit severe hearing losses.
BTE - Behind-the-Ear BTE models have recently become very popular due to the the very comfortable open fit style BTE hearing aids. Open fits are small BTE units which direct sound to the ear through a very thin tube inserted into the ear canal. Traditional BTE models use custom molds with larger diameter tubing and are the most flexible of any style hearing aid.