Cholinesterase is a family of enzymes that catalyze the hydrolysis of the neurotransmitter acetylcholine into choline and acetic acid, a reaction necessary to allow a cholinergic neuron to return to its resting state after activation. Cholinesterases are the target enzyme of numerous pesticides and chemical warfare agents and have been used for over two decades in the detection of these compounds. In this book, the authors present current research in the production, uses and health effects of cholinesterase. Topics discussed include cholinergic therapy for autistic spectrum disorders; acetylcholinesterase inhibitors in the treatment of Alzheimer’s disease; use of fish brain and muscle acetylcholinesterase as a biomarker to monitor water pollution and the evolutionary aspects of molecular forms and biological functions of acetylcholinesterase.