Among the many physical systems that form topological defects, liquid crystals are special because their characteristic topological defects are easy to visualize and manipulate. Many strategies can be employed to manipulate topological defects in these fluids with long-range order, either by external fields, or by choosing an appropriate topography of the confining surfaces, or dispersing colloidal particles in liquid crystals. Through combinations of these strategies, it is possible to generate defect arrays which then can be used for optics or to promote self-assembly of colloidal particles. I will discuss the behavior of a colloidal particle in liquid crystals next to an undulated surface, and the case of focal conic defects in smectic liquid crystals that can be assembled on curved interfaces to form an array of micro-lenses. I will also discuss defect arrays in nematic liquid crystals driven by electrical fields, which can form large, regular and reconfigurable structures.