Also called wry neck, torticollis is a condition where the head tilts to one side and often rotates slightly.  If you've ever had a crick in your neck, where you just feel stiff and unable to move your head and neck properly.  Imagine being like that for an extended period of time and you've experienced a similar symptom.  Typically, a major part of this condition is the tightening of what's called the strap muscle (technically named the sternocleidomastoid), which runs from just behind the ear down along the front part of your neck toward your sternum.  You have one on each side, so when that muscle tightens up (shortens/contracts) on one side, then it pulls and rotates your head. 
 

Unfortunately, the tightening of the strap muscle is usually the result of the problem; not the cause.  Much time and effort is spent addressing the muscle, but much like having to continually change a faulty tire on a car that has lost its alignment, it's only a temporary solution.  The reality is that an upper cervical/brainstem subluxation (misalignment of 1st or 2nd bone in neck) is a condition that directly causes changes in the strap muscles.  Initially creating a head tilt toward one side, the misalignment of the atlas (top) vertebra causes a change in muscle tone on either side.  One side gets scrunched up; the other gets stretched out.  Additionally, since that bone is held in place only by muscle and lacks an interlocking joint to hold it securely in place, it can cause the head to slightly rotate.  

The combination of head tilt and rotation is the cause of torticollis and is a direct result of a brainstem subluxation, which can be caused as early as the birthing process due to the traumatic forces of twisting and turning and yanking on the head/neck region.  The correction of this condition is quite simple and gentle.