EMDR is a "new" technique (in terms of the history of psychology).  As with many successes in our culture, it has been and continues to be controversial.  

We don’t know exactly how EMDR works, but we have a few ideas, especially in working with trauma.  So let's take trauma as an example.  When something overwhelming or traumatic happens, it seems to get locked in the nervous system with the experience of associated pictures, sounds, thoughts, feelings and so on.  The original experience may  get triggered when we encounter a reminder of the trauma or something that bears familiarity.  This triggering can create a lot or negative emotions, e.g., discomfort, fear, helplessness, and/or the like.  We may have, in essence, tapped into the old experience,  yet may or may not be aware that we have been triggered or are re-experiencing trauma. 

EMDR (originally Eye Movement Desensitization and Reprocessing) may be helpful in unlocking, reprocessing, and lessening the impact of unconscious and conscious traumatic material.  We have noted that eye movements seem similar to what happens in REM or dream sleep, which we know to be essential and beneficial for our functioning.  Eye movements to the light bar or other forms of bilateral stimulation (auditory, kinesthetic) seem to allow the brain to process the old experience albeit with a feeling of safety in the present time. 

Years ago, I took the EMDR training with my usual skepticism.  I was curious about what was in the early 90's "the latest technique."  EMDR had a good reputation among clinicians though based on anecdotal information.  Many in our field were critical of EMDR and even made fun of this (which to me suggested there was something to it!)

In my practice, I noticed that many clients with whom I tried EMDR were unusually  enthusiastic. They would return years later for EMDR.  As a practical person, I was content if EMDR were but a placebo--as long as it that worked for people.  

One day I was talking with a research-oriented psychologist with whom I often consult.  She and other with whom she works closely with had had very negative attitudes about EMDR for since its beginning.    I mentioned using EMDR with a client and started to qualify my use of this "unproven technique".  She stopped me mid-sentence and announced that based on recent research findings, EMDR works! 

As with anything, EMDR is not for every problems nor for everybody.  EMDR is a technique in context--which should not be practiced or utilized by just anybody.   At minimum, a starting point is a discussion of EMDR with a licensed mental health professional trained in and experienced with EMDR.