Agile methodologies emerged from small, co-located teams where trust developed organically through proximity, shared context, and frequent interpersonal interaction. As Agile has matured and been adopted at scale, often across distributed, multi-team, and global organisational environments, these implicit trust dynamics have been fundamentally disrupted. What once emerged naturally must now be deliberately designed. This chapter argues that trust represents a critical architectural, cultural, and leadership challenge. When trust is neglected, Agile risks devolving into ritualised compliance, where ceremonies persist but commitment, resilience, and learning erode. Drawing on organisational theory, Agile practice, and empirical insights, the chapter examines why trust becomes more fragile at scale, identifying structural complexity, weakened social ties, communication distortion, competing loyalties, and reduced psychological safety as key contributors. It then explores the foundational conditions required to sustain trust across teams, locations, and leadership layers, integrating structural enablers, communication patterns, and cultural practices. Common anti-patterns that corrode trust are analysed alongside practical strategies for leaders seeking to foster systemic trust through transparency, empathy, and intentional design. Ultimately, the chapter positions scaling trust as a deeply human endeavour and a prerequisite for sustainable agility. Without trust, Agile cannot thrive; with it, even highly complex systems can move with cohesion, clarity, and purpose.