At present, Chinese and foreign academic circles generally regard “communist society” and the “association of free individuals” as the same, and believe that the two concepts are exactly the same in Marx’s works. People are more familiar with communist society, but there are still some points that need to be clarified about the association of free individuals. First, the development of the concept of the association of free individuals in Marx’s text has gone through three stages: from the name of the republican state to the reference to the future society, and finally to the definition of the connotation of this concept. Only by seeing that it originates from modernity but is a rebellion against modernity can we grasp that its fundamental characteristic is criticality. Second, the association of free individuals and the communist society has similarities in three dimensions: both are rebellious concepts against modernity; both are scientific; and both have the same social form. Finally, the differences between the concepts of association of free individuals and communist society are compared from three perspectives: etymology, emphasis, and status. In terms of etymology, communist society emphasizes the collective, while the association of free individuals emphasizes the process of individual composition; communist society emphasizes totality and integrity, while the association of free individuals emphasizes relationality; in terms of status, communist society as the banner of communists is more fundamental and critical than the association of free individuals. Highlighting the differences between the two concepts helps further understand the tension between the individual and the community, Marx’s theory of social development, and the importance of the concept of association.