Indicator-based monitoring (IM) is crucial to support the uptake of Nature-based Solutions (NbS), to improve the knowledge of NbS benefits, and to promote evidence-based decision-making. Despite the growth of indicator frameworks to support practitioners in setting up IM processes for NbS, practitioners' perspectives and experiences of IM application, especially in relation to NbS, have been underexplored. We address this knowledge gap through an exploratory study on practitioners' decisions behind NbS-related IM through ten semi-structured interviews with experts from seven cities in the European (EU) and Latin American (LAC) region. LAC and EU practitioners use IM foremost to advocate the relevance and urgent need for improving urban sustainability. Novel compilations of eight applications of NbS-related IM in practice and three approaches to developing internally applied indicator frameworks were identified. More consideration of social indicators, technical feasibility, legitimacy, and temporal scales is needed for better and more inclusive NbS-related IM in practice.