Dark matter is a hypothetical kind of matter that cannot be seen with telescopes but would account for most of the matter in the universe. The existence and properties of dark matter are inferred from its gravitational effects on visible matter, radiation, and the large-scale structure of the universe. Dark matter has not been detected directly, making it one of the greatest mysteries in modern astrophysics. Dark matter neither emits nor absorbs light, or any other electromagnetic radiation, at any significant level. According to the Planck mission team, and based on the standard model of cosmology, the total mass-energy of the known universe contains 4.9% ordinary matter, 26.8% dark matter and 68.3% dark energy. Thus, dark matter plus dark energy is estimated to constitute 95.1% of the total mass-energy content of the universe. This book discusses the latest information regarding "Dark Matter."