The idea that Parkinson’s disease involves more than its classic motor symptoms (tremor, slowness, shuffling, etc.) is not new. Even James Parkinson recognized this in his seminal publication describing this disease in 1817. However, it is only in the last 25 years or so that neurologists have taken a serious, in-depth look at the nonmotor manifestations of Parkinson’s disease. What they have found has evolved into a rich field of study that has both permitted a greater understanding, and revealed greater levels of complexity, of Parkinson’s disease than previously known. ...