Scrum is often praised for its structure and efficiency, but its true effectiveness hinges on something far less tangible: trust. This chapter explores how open communication serves as the foundation for trust in Agile teams, enabling psychological safety, team cohesion, and continuous learning. Drawing from organisational theory, behavioural science, and Agile practice, the chapter examines how trust is built through structured events and artefacts but also through day-to-day interactions marked by honesty, integrity, and transparency. It highlights the critical role of organisational culture, identifying barriers such as fear, hierarchy, and cultural silence that constrain open dialogue. Conversely, it outlines enabling conditions, like psychological safety, feedback culture, and inclusive norms, that foster trust and high performance. By distinguishing between transactional communication and transformational dialogue, and between high-trust and low-trust patterns, the chapter offers a practical lens for diagnosing team health and enhancing collaboration. Ultimately, it argues that open communication is the operating system of Agile. Without it, Scrum devolves into ritual; with it, teams unlock agility, resilience, and genuine innovation.