Huperzine A (HupA), isolated originally from a traditional Chinese medicine Qiang Ceng Ta, whole plant of Huperzia serrata (Thunb. ex Murray) Trev., a member of the Huperziaceae family, has attracted intense attention since its marked anticholinesterase activity was discovered by Chinese scientists. Several members of the Huperziaceae (Huperzia and Phlegmariurus species) have been used as medicines in China for contusions, strains, swellings, schizophrenia, myasthenia gravis and organophosphate poisoning. HupA has been marketed in China as a new drug for Alzheimer's disease (AD) treatment and its derivative ZT-1 is being developed as anti-AD new drug candidate both in China and in Europe. A review of the chemistry, bioactivities, toxicology, clinical trials and natural resources of HupA source plants is presented.