<p>Concentration in the Spanish publishing sector has significantly increased over the past three decades, driven by major groups such as Planeta and Penguin Random House through their acquisition of small and medium-sized publishers. However, this consolidation raises concerns about the decline of literary diversity and the potential homogenization of content, as these large companies tend to prioritize commercial titles, thereby limiting the representation of emerging and minority authors. This study examines the evolution of concentration using indicators such as the CR4/CR5 ratios and the Herfindahl-Hirschman Index (HHI), which reveal a consistent rise in concentration levels, reflecting the growing dominance of these major publishers. Despite the challenges, independent publishers remain crucial to fostering diversity and innovation in the sector by focusing on niche markets and taking risks on unconventional works. The study concludes with recommendations for policies that support these independent publishers and promote competition, ensuring a diverse and creative publishing ecosystem. Addressing the challenges posed by concentration is essential to maintaining a healthy publishing environment that encourages a plurality of voices and creativity. </p>