行动主义（英语：Activism），这个词的来源于「Active」（活跃），所以又可以翻译成活跃主义。这个词主要形容一个圈子 一个社会之中那些比较活跃的分子。经常带头或者主动的存在一个组织中去带领（或者不带领）一些活动或者发表一些自己的见解。

但这个定义在应用中比较广泛。比如激进主义和行动主义在应用中就比较模糊。又比如政治行动主义 （Political Activism）．　他的表现主要体现在对当今的政治进行一些激进的批判 （Critique）。现在这些人主要活跃于网络上，但又不是一种反政府，而是犀利的批判。第一次世界大战后欧洲表现主义知识分子的政治行动原则也常被称为行动主义。20世纪60年代，青年政治行动主义就是其中的一个例子，1967-1968年间，美国、西德、法国、意大利等地的大学都爆发了各种示威活动，与警察的冲突也屡见不鲜。

Activism consists of efforts to promote, impede, or direct social, political, economic, or environmental change, or stasis with the desire to make improvements in society and to correct social injustice. Forms of activism range from writing letters to newspapers or to politicians, political campaigning, economic activism such as boycotts or preferentially patronizing businesses, rallies, street marches, strikes, sit-ins, and hunger strikes. One can also express activism through different forms of art. Daily acts of protest such as not buying clothes from a certain clothing company because they exploit workers is another form of activism. One view holds that acknowledging privileges and oppressions on a daily basis ranks as a form of activism. Research has begun to explore how activist groups in the United States and in Canada use social media to facilitate civic engagement and collective action.