Over 150 molecules and ions have been so far identified in the interstellar space. Ions play dominant role in the interstellar chemical reactions. In total 16 cations (CH+, CO+, SO+, HCO+, HCS+, HOC+, N2H+, H3+, H2D+, CH2D+, HCNH+, HOCO+, H3O+, H2COH+, HC3NH+) were found. Chemical reactions in the interstellar space are connected to reactions of cations, and the presence of anions was theoretically predicted. In 2006 their existence was confirmed observationally.