Do Christians need to be socialists? Karl Barth and socialism. In this article, the author deals with a “shadow side” of the life and work of Karl Barth. From the perspective of many Eastern and Central European people who have experienced “real” socialism, the right to ask the question posed in the title is evident. It examines under what influences Karl Barth’s inclination towards social democracy and socialism arose. Three circumstances are mentioned: 1. The traditional Swiss solidarity and social sensitivity for the cause of the weak and oppressed. Karl Barth received this sensitivity, so to speak, in his parents’ house. 2. The three theologians of “religious socialism” (Christoph Blumhardt, Hermann Kutter, and Leonhard Ragaz) had a great influence on Barth. 3. It is described in more detail how Barth’s attitude towards socialism was kindled, so to speak, as a counter-reaction to the “raging” anti-communism in Switzerland (but generally throughout Western Europe and North America). In this context, the problem of “Barth’s silence on the Hungarian Uprising of 1956” is also addressed. In the final chapter, the author attempts to theologically justify Barth’s attitude towards socialism based on some quotes from the section “The Active Life” (Das tätige Leben; KD III/4).