Billie Tsien and Tod Williams discuss their core beliefs and design principles, illustrating them with examples from their work. They stress topography, the presence of the human hand, rethinking material, the specificity of place, and he primacy of the interior. They describe in detail four recent projects: the Barnes Foundation (2012), the Asia Society Hong Kong Center (2011), the Tata Consultancy Services (2015), and the LeFrak Center ice rink in Prospect Park (2013).