Implementation of school-based collaboration is both complex and contextual. In this article, the authors conducted a systematic review of the literature to identify the factors that facilitate or discourage school-based collaboration in secondary schools. As a result, they identified 50 studies that highlight the complexities of fostering effective teacher collaboration in secondary schools. Reviewing the studies, they identified three types of collaborative learning activities: sharing, experimenting, and designing. Despite the popularity of collaboration, the study emphasizes that simply providing more time or reducing top-down control is insufficient. Key findings include several insights. First, process matters; how teachers work together is crucial for successful collaboration. Second, context matters; school culture, leadership, and individual teacher characteristics influence collaboration outcomes. Recommendations include starting with process and paying attention to context. Leaders can prioritize process by creating opportunities for teachers to deeply explore and analyze pedagogy and learning practices. Schools should assess their current situation before adopting new collaboration strategies and then integrate teacher characteristics and school culture into collaboration initiatives. Ultimately, the review suggests that successful teacher collaboration is deeply rooted in the school context and requires a nuanced approach.