Eyewear having three-dimensional (3D) viewing capability is disclosed. The 3D eyewear can include eyeglasses and an eyewear attachment configured to attach to the eyeglasses. The eyeglasses can have lens elements that include linear polarizers, and can be worn by the user without the eyewear attachment during everyday use. The eyewear attachment can include auxiliary lens elements that include quarter-wave plates oriented such that auxiliary lens elements of the eyewear attachment and the lens elements of the eyeglasses cooperate to function as circular polarizers. One lens pair can function as a circular polarizer configured to filter out right-handed circularly polarized light, and the other lens pair can function as a circular polarizer configured to filter out left-handed circularly polarized light. Thus, when the eyeglasses are worn with the eyewear attachment attached thereto, they can function as 3D eyewear to present right-eye and left-eye images, which are displayed using oppositely oriented circularly polarized light, to the respective right or left eye of the wearer. In some embodiments, the auxiliary lens elements can removably attach directly to the lens elements of the eyeglasses.