The volume Optimism and Architecture presents the awarded and shortlisted projects for the Aga Khan Award for Architecture 2025. The book explores the myriad ways in which optimism and hope are fundamentally linked to better design outcomes, highlighting architecture's capacity to serve as a catalyst for pluralism, social transformation, cultural dialogue, and climate-responsive design. Unpublished material offers deep insights into the broad social, political, and cultural contexts that shape our built environments. The publication sheds light on the extensive jury and in-depth review processes for which the Award is renowned. Through essays and conversations, this volume examines how architecture can reinvigorate tradition through thoughtful innovation, connect local practices with global conversations, touch the earth lightly yet profoundly, and create inclusive spaces where diverse cultures and histories converge. Architecture is considered not only as a physical structure but also as a cultural practice that shapes public life, sparks social engagement, and reimagines heritage and identity in a rapidly changing world. This publication provides an optimistic and vivid portrait of contemporary architecture's role in fostering more inclusive and interconnected futures. With contributions by Azra Akšamija, Lucia Allais, David Basulto, Farrokh Derakhshani, Yvonne Farrell, Hanif Kara, Yacouba Konaté, Lesley Lokko, Raafat Majzoub, Deen Sharp, and Cristina Steingräber.