Open access publishing is a milestone in the history of academic dissemination, and ACP has been at the forefront of this movement. This paper is co-authored by four scientists who played key roles in initiating ACP, and establishing and maintaining it as a leading journal in atmospheric science. It articulates the vision of 'open science' that motivated the establishment of ACP and provides a comprehensive overview of the publication process of ACP and other EGU journals and how open science is enabled and promoted within that process. Detailed statistics and commentary reveal how open science practices in publication in EGU journals have developed and evolved over the last 25 years, and how this may continue to develop into the future.