The synthesis of nanoparticles of controlled size and shape has attracted much recent interest (1–6). One promising route to nanostructured materials involves synthesis in lyotropic liquid crystals (7–10) formed by mixing a solvent, usually water, and an amphiphile, typically either an ionic or non-ionic surfactant. These amphiphilic molecules typically consist of covalently bound hydrophobic and hydrophilic segments. When such amphiphilic molecules are mixed with water, the resulting amphiphilewater systems self organize into structured periodic lattices consisting of nanometer sized hydrophobic and hydrophilic domains in order to minimize free energy (11). Lyotropic liquid crystals are of exceptional interest because the size, shape, symmetry, and connectivity of these self organized nanoreactors can be predetermined through appropriate selection or design of the liquid crystal phase. Important for scale-up, these nanoreactors are easily reproducible, and can be generated in large volume. When these nanoreactors are used for materials synthesis, it is the subtle interplay of the “soft” nanoreactors with the growing inorganic phase that determines the final size, shape, and crystallographic orientation of the resulting nanomaterials. Liquid crystal nanoreactors are exceptionally versatile for materials synthesis, because there are many chemistries that can be designed to operate exclusively within either the hydrophilic or hydrophobic domains of the liquid crystal. The nanomorphology of the resulting inorganic product is thus greatly influenced by the geometric properties of the nanoreactors it was associated with. Here, we explore the effect of two liquid crystalline phases on the synthesis of BiOCl, the first being a three-dimensionally percolated hexagonal liquid crystal, and the second, a two dimensionally percolated lamellar liquid crystal. Both systems were chemically similar, the only difference being the relative ratio of amphiphile to water, the two components that made up the liquid crystal. We compare these results with synthesis in an isotropic fluid. The size and shape of the BiOCl product correlated directly with the connectivity and confinement effects of the two liquid crystals. The three dimensionally interconnected hexagonal phase yields fairly monodisperse 250 nm long arrowhead shaped particles, while the two dimensionally connected lamellar, phase yields roughly spherical 5 nm particles. Particles synthesized in the absence of the liquid crystal had a completely different shape, and were highly polydisperse in size, consisting of disks ranging from 50 to 250 nm in diameter. Scripta mater. 44 (2001) 1893–1897