As a Traditional Chinese Medicine, Artemisia annua L. (A. annua) has been used for the treatment of various diseases since ancient times, including intermittent fevers due to malaria, bone steaming and heat/fever arising from exhaustion, tuberculosis, lice, wounds, scabies, dysentery et al. With the discovery of artemisinin and its excellent anti-malarial activity, A. annua has received great attention. Recently, A. annua has been revealed to show inhibitory effects against parasites (e.g. Plasmodium, Toxoplasma gondii, Leishmania, Acanthamoeba, Schistosoma), viruses (e.g. hepatitis A virus, herpes simplex viruses 1 and 2, human immunodeficiency virus), fungi (Candida, Malassezia, Saccharomyces spp.) and bacteria (Enterococcus, Streptococcus, Staphylococcus, Bacillus, Listeria, Haemophilus, Escherichia, Pseudomonas, Klebsiella, Acinetobacter, Salmonella, Yersinia spp.). A. annua has also been reported to possess anti-inflammatory and anti-cancer actions and been employed for the treatment of osteoarthritis, leukemia, colon cancer, renal cell carcinoma, breast cancer, non-small cell lung cancer, prostate cancre and hepatoma. Besides, the immunoregulation, anti-adipogenic, anti-ulcerogenic, anti-asthmatic, anti-nociceptive and anti-osteoporotic activities of A. annua were also evaluated. Along these lines, this review summarizes the traditional application and modern pharmacological research of A. annua, providing novel insights of A. annua in the treatment of various diseases.