A METATOY is a sheet, formed by a two-dimensional array of small, telescopic optical components, that switches the path of transmitted light rays. METATOY is an acronym for "metamaterial for rays", representing a number of analogies with metamaterials; METATOYs even satisfy a few definitions of metamaterials, but are certainly not metamaterials in the usual sense. When seen from a distance, the view through each individual telescopic optical component acts as one pixel of the view through the METATOY as a whole. In the simplest case, the individual optical components are all identical; the METATOY then behaves like a homogeneous, but pixellated, window that can have very unusual optical properties (see the picture of the view through a METATOY). METATOYs are usually treated within the framework of geometrical optics; the light-ray-direction change performed by a METATOY is described by a mapping of the direction of any incoming light ray onto the corresponding direction of the outgoing ray. The light-ray-direction mappings can be very general. METATOYs can even create pixellated light-ray fields that could not exist in non-pixellated form due to a condition imposed by wave optics. Much of the work on METATOYs is currently theoretical, backed up by computer simulations. A small number of experiments have been performed to date; more experimental work is ongoing. Examples of METATOYs Telescopic optical components that have been used as the unit cell of two-dimensional arrays, and which therefore form homogeneous METATOYs, include a pair of identical lenses (focal length ) that share the same optical axis (perpendicular to the METATOY) and that are separated by , that is they share one focal plane (a special case of a refracting telescope with angular magnification -1); a pair of non-identical lenses (focal lengths and ) that share the same optical axis (again perpendicular to the METATOY) and that are separated by , that is they again share one focal plane (a generalization of the former case, a refracting telescope with any angular magnification); a pair of non-identical lenses (focal lengths and ) that share one focal plane, that is, they share the direction of the optical axis, which is not necessarily perpendicular to the METATOY, and they are separated by (a generalization of the former case); a prism; and a Dove prism Examples of inhomogeneous METATOYs include the moiré magnifier, which is based on deliberately "mis-aligned" pairs of confocal microlens arrays; Fresnel lenses, which can be