To study perceptual grouping processes, vision scientists often use stimuli consisting of spatially separated local elements that, together, elicit the percept of a global structure. We developed a set of methods for constructing such displays and implemented them in an open-source MATLAB toolbox, GERT (Grouping Elements Rendering Toolbox). The main purpose of GERT is to embed a contour in a field of randomly positioned elements, while avoiding the introduction of a local density cue. However, GERT's modular implementation enables the user to create a far greater variety of perceptual grouping displays, using these same methods. A generic rendering engine grants access to a variety of element-drawing functions, including Gabors, Gaussians, letters, and polygons.