Chemistry, pharmacology and applications of compounds inhibiting enzymatic acetylcholine (ACh) degradation are reviewed. Acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), or non-specific cholinesterase, are members of the family of cholinesterase (ChE), the ACh degrading enzymes. ChE inhibitors (is) are compounds inhibiting reversibly or irreversibly enzymatic ACh breakdown. The first ChE-is were organophosphate derivatives, synthesized as neurotoxic agents. These compounds cause toxic accumulation of ACh at the central and autonomic nervous system level and induce several neurological and autonomic effects including ataxia, seizures, coma, and respiratory depression. This strong toxicity is the reason of their identification as warfare agents. The subsequent main use of ChE-is was as pesticides. ChEs are important enzymes needed for proper functioning of insect nervous system. Although ChE-is are intended for insect pests, in some situations they can be poisonous or toxic to humans. The most recent and promising use of AChE/BuChE-is was symptomatic treatment of cognitive dysfunction occurring in Alzheimers disease (AD). Forebrain cholinergic system has a key role in learning and memory and AD is characterized by brain cholinergic impairment. AChE/BuChE-is are the first drugs approved for symptomatic treatment of cognitive deficits in AD. Besides cognitive relief induced in mild-to-moderate AD, increasing evidence suggests that ChE-is may interfere with the progression of the disease. If this hypothesis will be supported by ongoing studies, these compounds could become a disease-modifying strategy in the treatment of adult-onset dementia.