An ongoing program of temporary structures designed by internationally acclaimed architects, The Serpentine Gallery Pavilion commission was conceived by the institution's director, Julia Peyton-Jones, in 2000, and is unique worldwide. The Pavilion for 2009 was designed by Kazuyo Sejima and Ryue Nishizawa, of the leading Japanese architecture practice SANAA. Sejima and Nishizawa created a stunning structure that resembles a reflective cloud or a pool of water, sitting atop a series of delicate columns. The metal roof varies in height, wrapping itself around the trees in the park and sweeping down almost to the ground in some places. Open and ephemeral in structure, its reflective materials allow it to sit seamlessly within the natural environment, reflecting both the park and sky. "It works as a field of activity with no walls," say Sejima and Nishizawa. This publication documents the conception, construction and life of this impressive temporary structure.