Diatoms are an extraordinarily successful group of organisms and their many thousands of species have diversified and specialized so as to occupy every environmental niche. Part of their success derives from their unique protective cell walls, beautifully elaborate structures made of pure silica. However, living inside walls made of this rigid, refractory material creates many problems. Just how diatoms circumvent these problems provides the major theme in this spectacular exploration of the biology of living cells. Many of the phenomena illustrated are surprising and have never been recorded before. There is much here for the specialist, student, and anyone interested in an intimate view of life at the cellular level.