Gradient index (GRIN) lenses are more common than you may know. The human lens is a gradient index optic, and the last time you scanned a document the scanner probably used a gradient index lens array. In a homogeneous lens, light refracts at the surfaces, only bending when it enters and exits the material. In a GRIN lens, light refracts at the surfaces and also bends inside the lens. The ability of GRIN optics to bend light gives an optical designer more variables to work with and opens up new design spaces. This course is designed to introduce optical designers and engineers to existing and emerging GRIN materials and to teach them the essentials necessary to use GRIN materials in optical designs. This course begins with an introduction to gradient index phenomenon and the basic principles of GRIN optics. The properties of axial, radial and spherical optical systems will be presented as will a review of aberration theory. A variety of GRIN materials that cover wavelength bands from the visible to the long wave infrared will be discussed. GRIN chromatic properties will be reviewed, and the GRIN Abbe number will be introduced. The course will review software tools written to help optical designers use GRIN materials in their systems along with easy-to-understand examples.