The cyanamides form a class of compounds isoelectronic with the azides. They are, however, more stable to heat and ionizing radiations. A detailed study has been made of the optical and electrical properties of small single crystals (of dimensions several micrometres) in order to determine the nature of the bonds in the sodium, thallium, silver, and lead salts. Structural data are also available and it is concluded that while sodium cyanamide is an ionic solid, silver and lead cyanamides are covalent and thallium cyanamide at room temperature is probably also a covalent solid. The nature of the bonds of the metal atom to the nitrogen of the cyanamide group can, however, be different in the thallium silver and lead salts and this will be reflected in the order of the stability of the solids. It is found that ionizing radiations can introduce colour centres into sodium cyanamide, but only minor effects are observed with the other solids. It is suggested that electronic processes will be involved in the solid state decomposition of sodium cyanamide but bond fission will be the first step in the decomposition of the covalent cyanamides.