This chapter addresses the evolution of media and communication concentration, its causes, and its consequences. The political relevance of this perennial problem has amplified over the past decade, but it is still largely ignored by politics. The scholarly social science discourse has determined time and again how media ownership concentration controls editorial boards and newsrooms, curtails content diversity, marginalises less popular and consequently expensive content, and commodifies cultural industries altogether. Despite this, the concentration of media ownership remains one of the least-regulated media policy issues of the last three decades. Metrics undeniably demonstrate continuous growth of ownership concentration at the global, national, and local level. Digitalisation has not counterbalanced power relations in society at large; rather, digital communication platforms reflect and replicate dominant media structures. Lately, however, policy initiatives have emerged to address the negative effects of ownership concentration in the media sector.