The in vitro antimicrobial and anti-inflammatory activities of extracts, essential oils and some compounds isolated from six species of genus Nigella, namely N. arvensis, N. damascena, N. nigellastrum, N. hispanica, N. orientalis, and N. sativa, are described in this work. The antimicrobial activities of extracts from seeds of N. arvensis and N. orientalis, as well as chemical composition of essential oils from seeds of both species are reported here. The significant influence of four different extraction methods on the antimicrobial activity and chemical composition of N. sativa seed essential is also described. In addition, the anti-inflammatory effect of four components of N. arvensis seeds, namely dithymoquinone, thymohydroquinone, thymol and thymoquinone, has been detected as a result of this research. This work also summarizes the current knowledge on botany, origin, geographical distribution, uses, biological effects and chemistry of all six species. Some suggestions for further research on chemical and pharmacological properties are also given.