等离子体天体物理学是以等离子体物理学为基础的天体物理学分支。宇宙中绝大部分物质是等离子体，因此等离子体天体物理学的研究范围很广，包括日冕、超新星遗迹、活动星系核、致密星、星际介质等。

在1929年美国物理学家朗缪尔提出等离子体这个概念之前，天体物理学家已经研究过等离子体。1921年米尔恩（Milne）根据萨哈公式创建了恒星大气理论，1939年丹麦天文学家斯特龙根提出星际介质中存在中性氢区和电离氢区，对星际介质和恒星演化理论起了重要的影响。等离子体天体物理学这个名词是在20世纪60年代末出现的。等离子体天体物理学采用实验室等离子体物理学取得的成果，本身也可以得到对等离子体物理学有意义的新结果。

An astrophysical plasma is a plasma (a highly ionized gas) whose physical properties are studied as part of astrophysics. Much of the baryonic matter of the universe is thought to consist of plasma, a state of matter in which atoms and molecules are so hot, that they have ionized by breaking up into their constituent parts, negatively charged electrons and positively charged ions. Because the particles are charged, they are strongly influenced by electromagnetic forces, that is, by magnetic and electric fields. All astrophysical plasmas are likely influenced by magnetic fields.