Scientific research has become increasingly complex, and the process demands advanced infrastructure, specialized tools, and interdisciplinary planet-wide collaboration. While these developments have enabled major breakthroughs with undisputed societal benefits, they have also widened existing inequalities across the global research ecosystem. Open Science (OS) has emerged as a response to these challenges, promoting transparency, reproducibility, and inclusivity. Yet, despite important progress, access remains uneven. This work examines the persistent and emerging barriers that hinder full participation in science, especially for researchers in low- and middle-income countries (LMICs). We analyse key steps of the research process: from access to experimental tools, software, protocols, and data, to training, publishing, and translation to societal impact. We highlight the role of open hardware, software, community protocols, and locally grounded training initiatives in broadening participation and improving reproducibility. At the same time, we show how structural issues such as prohibitive publishing costs, uneven funding, language barriers, and inadequate support for hands-on training, limit the reach of OS efforts. By foregrounding participation and equity, we call for a redefinition of openness not merely as free access to outputs, but as a system-wide practice rooted in shared infrastructure, fair policy, and mutual responsibility. Realizing the promise of OS will require sustained commitment to structural reform, inclusive collaboration, and investment in global scientific capacity.