A mega-journal is a peer-reviewed scientific open-access journal designed to be much larger than a traditional classical journal. The low selectivity review criteria largely focused on the scientific soundness of the research methodology and ethical issues regardless of the importance and application of the results, the fast peer review, and a very broad scope usually covering a whole discipline, such as biomedicine or social science, are the major hallmarks. This publishing model was pioneered by PLOS One and was soon followed by other publishers. A few years ago, it was believed that the academic journal landscape would dominate by the mega-journals model, but a decline has been registered in the last few years. This editorial aimed at presenting the current state-of-the-art of the open-access mega-journals (OAMJs) in scientific publications.