Lithium, the most thoroughly researched bipolar medication, is mentioned by name in the titles of 10 of the 19 chapters. It is eminently clear that lithium has many "mechanisms of action," or, as succinctly put by Mogens Schou, "Since the key is so small, it fits into many locks" (1). If something affects virtually everything, determining which aspect(s) of this multiplicity of mechanisms is responsible for antimanic, antidepressant, and prophylactic properties is a daunting challenge. The search would be simplified greatly, of course, if the etiology of bipolar disorder were not such a mystery.