在宇宙学中，暗物质（dark matter），是指无法通过电磁波的观测进行研究，也就是不与电磁力产生作用的物质。人们目前只能透过重力产生的效应得知，而且已经发现宇宙中有大量暗物质的存在。

现代天文学经由重力透镜、宇宙中大尺度结构的形成、微波背景辐射等方法和理论来探测暗物质。而根据ΛCDM模型，由普朗克卫星探测的数据得到：整个宇宙的构成中，我们常说的物质占4.9%，而暗物质则占26.8%，还有68.3%是暗能量（质能等价）。暗物质的存在可以解决大爆炸理论中的不自洽性（inconsistency），对结构形成也非常关键。暗物质很有可能是一种（或几种）粒子物理标准模型以外的新粒子所构成。对暗物质（和暗能量）的研究是现代宇宙学和粒子物理的重要课题。

Dark matter is a hypothetical type of matter composing the approximately 27% of the mass and energy in the observable universe that is not accounted for by dark energy, baryonic matter, and neutrinos. The name refers to the fact that it does not emit or interact with electromagnetic radiation, such as light, and is thus invisible to the entire electromagnetic spectrum. Although dark matter cannot be directly observed with conventional electromagnetic telescopes, its existence and properties are inferred from its various gravitational effects such as the motions of visible matter, via gravitational lensing, its influence on the universe's large-scale structure, and its effects in the cosmic microwave background. Dark matter is transparent to electromagnetic radiation and/or is so dense and small that it fails to absorb or emit enough radiation to be detectable with current imaging technology.