Citizen science platforms (CSPs) and citizen observatories (COs) are rapidly expanding research infrastructures (RIs) that support the growth of citizen science. These systems have boosted data collection capabilities and broadened participant engagement across spatial and demographic dimensions. Despite their essential role in advancing citizen science, the current state of knowledge of these infrastructures remains largely unexplored, affecting both theoretical understanding and practical implementation. The study discussed herein addresses this knowledge gap through a systematic review of 474 articles, with in-depth analysis of 72 publications spanning a 15-year period across multiple disciplinary domains. The methodological framework integrates bibliometric analysis with qualitative investigation, utilizing Web of Science and Scopus databases, supplemented by grey literature from Zenodo and Google Scholar. Findings indicate that research in this field has developed across three main waves: technological development and engagement, monitoring systems and openness, and frontiers technologies. This evolution reflects a progression in the CSP body of knowledge from technical documentation to complex socio-technological systems. Analysis of 450 articles identified 98 unique terms referring to CSPs, highlighting conceptual fragmentation. To clarify the landscape of overlapping, we propose a CSP purpose-based taxonomic framework comprising nine platform categories, contributing to a clearer understanding of the CSPs’ role in citizen science. Additionally, our systematic analysis reveals key research trajectories essential for strengthening CSPs and COs as sustainable infrastructures.