Contrary to a widespread belief that open access publications are paid by their authors, a significant amount of scientific articles are published with no fees to both readers and authors (or “Diamond” model). In 2021, it is estimated that between 17,000 and 29,000 scientific journals rely on a Diamond model. 73% of the journals registered in the Directory of Open Access Journals charge no fee. The Diamond model is attested on a world wide scale. It is especially prevalent in Latin America (95% of journals) following the emergence of large publicly-supported platforms, such as SciELO and Redalyc and to a lesser extent in Eastern Europe and South-East Asian countries like Indonesia. Diamond journals are frequently embedded in local communities of researchers, non-academic professionals and private citizens: they play an important role in the circulation of knowledge and in the preservation of linguistic diversity in science. Diamond journals are an efficient economic model. The median cost per article is estimated at $200, or 1/6th of the expenses of commercial journals. Most of their funding is covered by a variety of non-commercial support: recurrent funding, grants, technical support, volunteer work. Diamond journals are also less productive than commercial journals. They represent a lower output of academic articles overall, making up less than half of all publications indexed by the Directory of Open Access Journals. While the concept of “diamond journal” was only introduced in 2011, community-owned scientific journals have a long history. A variety of common-based structures from subsidized university publishers to volunteer-run cooperatives have existed for decades and been revived by the development of open science in the late 1990s. Reliance on communities is one of the main strengths of Diamond journals. Although they are measurably a major model of open science publishing, diamond journals have long been little acknowledged by academic policies and funders. Leading indexes like the Web of Science or Scopus tend to favor commercial publications. Archiving has been identified as a major concern, as several publications can remain unnoticed from the main preservation initiatives. In 2022, new national and international policies, such as the UNESCO recommendation on open science, or the action plan for diamond Open Access supported by cOAlition S aims to support the development of Diamond journal. Diamond journals are increasingly part of an emerging ecosystem of “scientific commons” alongside open science infrastructures, free academic software, open data programs or open metrics.