There are five common styles of hearing instruments.  All five help with mild to moderate
hearing losses, but if your loss is severe, choices may be limited. 

While size is the most obvious difference, each style has different attributes that are
important to consider.  In most cases style or size of the hearing instrument is chosen
separately from the circuit, or sound processor.  What you see doesn't determine the
sound you hear. 

On-the-Ear (OTE) or Open

On-the-Ear instruments also referred to as "open" instruments
offer a combination of convenience and comfort.  They are
very light and discreet in design, hiding comfortably on top of
the ear.  The unique OTE design allows testing and fitting in
the same visit, so you can experience better hearing in one day. 

Completely-in-the-Canal (CIC)

Completely-in-the-Canal instruments are the smallest and most
discreet custom instruments available.  CICs are designed to fit
entirely in the ear canal, improving sound quality and reducing
feedback.  CICs are popular for their aesthetic appeal, but are
not appropriate for everyone.

In-the-Canal (ITC)

In-the-Canal instruments are custom designed to fit in the ear
canal.  ITCs are discreet, yet still slightly visible within the outer
ear.  ITC instruments offer a variety of options that would have
previously required a larger model.

In-the-Ear (ITE)

In-the-Ear instruments house a variety of circuit options in a
custom-made shell designed to fit in the outer portion of the
ear.  Its size and easy-to-use controls may also be helpful
for people with limited dexterity.

Behind-the-Ear (BTE)

Behind-the-Ear hearing instruments are the largest and offers more
power than most custom models.  BTEs rest behind the ear and
sound is sent to the ear canal via clear plactic tubing and an
earmold which is molded to fit comfortably in the outer ear area.