The holographic optical tweezers have been developed that can manipulate many particles simultaneously in three dimensions in order to create micro-crystal structures that extend over many tens of microns. The technique uses specific hologram-design algorithms to create structures that can be dynamically scaled or rotated about arbitrary axes. The generation and control of pre-determined crystal-like structures have significant potential in fields as diverse as photonic-crystal construction, seeding of biological tissue growth and creation of metrological standards within nanotechnology.