Amidoximes are compounds bearing both a hydroxyimino and an amino group at the same carbon atom which makes them versatile building blocks for the synthesis of various heterocycles. Their importance in chemistry along with their rich biology, make amidoximes an attractive target for medicinal chemists, biochemists and biologists. Amidoximes and simple O-substituted derivatives possess very important biological activities functioning as antituberculotic, antibacterial, bacteriostatic, insecticidal, elminthicidal, antiviral, herbicidal, fungicidal, antineoplastic, antiarrythmic, antihypertensive, antihistaminic, anxiolytic-antidepressant, anti-inflammatory/ antioxidant, antiaggregatory (NO donors) or plant growth regulatory agents. A number of amidoximes has already been used as drugs, or currently being in clinical trials. Their numerous pharmaceutical applications have been recently enriched, due to the fact that some mechanistic pathways, concerning their conversion to amidines, as well as their ability to release NO were clarified, giving a new insight to their mode of action and allowing the design of new therapeutic agents. The main subject of the present review paper is to highlight aspects concerning chemical and biological questions on this interesting class of compounds. Some new synthetic methodologies as well as improvements of previously reported general reactions involving amidoximes, acylated amidoximes, and amidines are presented. The biological applications of amidoximes over the end of 2006 are also extensively reviewed.