Cyanide is an omnipresent substance in the environment and may have been present in the chemical evolution of processes before the appearance of life on Earth. Nowadays this compound is released by several methods, including acrylic and ammonia manufacturing, electroplating, steel production, the extraction of gold and silver, and jewelry. Hydrocyanic acid is also found in smoke, and it is generated by the incomplete combustion of carbon compounds in fires, cigarettes and propulsion motors. Furthermore, over 2, 500 plant species are known to accumulate cyanide. In this book, the authors present several aspects of cyanide. In the first chapter, the role of cyanide in the chemical evolution process on early Earth and beyond our planet is discussed. The toxicity of cyanide to animals and humans are presented in Chapter 2. In the third chapter, the author outlines a phenomenological method to estimate the hydrogen cyanide generation. The last chapter is a review of the use of cyanide-bridged coordination polymer electrodes in electrode materials of rechargeable batteries.