Elastomeric optics exploit light transparent, variable translucent, and reflective stretchable polymers to create novel strain-tunable optical elements and flexible multifunctional optical sheets. Optical sheets are thin, large-area polymer light guide structures that can be used to create a wide variety of passive light harvesting and illumination systems. The book introduces the theoretical principles of elastomeric optics and explores how simple and complex mechanically deformable optical devices can be designed and fabricated. The transmission of light through these optical components or waveguides depends on the selected materials, surface interface, geometric design, optical coupling of embedded micro-structures, and degree of device deformation. In addition to providing a technical foundation for building adaptable optics, the book seeks to inspire the next generation of scientists and engineers to develop innovative solutions far beyond anything imagined today.