青年马克思作品中论及的异化（Entfremdung，又译疏离），是指原本自然互属或和谐的两物彼此分离、甚至互相对立。异化一词最重要的用法是表示人与其「类本质」（Gattungswesen）的异化。马克思主张异化是资本主义的结果，他的立论基于路德维希·安德列斯·费尔巴哈在《基督教的本质》（1841年）中提出的理论，费尔巴哈在此书中力证「上帝」观念是人类特征的异化；麦克斯·施蒂纳则进一步主张「人性」观念是个人的异化；马克思与恩格斯在《德意志意识形态》（1845年）中反驳了他的观点。

Alienation, a sociological concept developed by several classical and contemporary theorists, is "a condition in social relationships reflected by a low degree of integration or common values and a high degree of distance or isolation between individuals, or between an individual and a group of people in a community or work environment". The concept has many discipline-specific uses, and can refer both to a personal psychological state (subjectively) and to a type of social relationship (objectively).