The formation of two types of photonic crystal is described. Normal opal is formed by close packing of silica spheres. The synthesis of the silica spheres is described and some of the factors that influence the size of the spheres in the product are discussed. Three different methods for the preparation of close packed arrangements of the spheres are described and the photonic properties of the crystals produced are demonstrated. Inverse opal is based on a close packed array of “air” spheres in a dielectric matrix. Different methods for the formation of this ordered microporous solid based on titanium dioxide are described and the photonic properties of this material are discussed.