Roles and optical responses of microlenses in information optics applications will be discussed. Microlenses can be found from semiconductor fabrication tools to tiny imaging apparatuses equipped in smart electronic devices, therefore, their functionalities and sizes are manifold. We discuss the scaling behavior of micro-optical elements and optical responses in different characteristic sizes. We investigate the transition of optical regime and define the boundary between them, named “refraction limit”. At the end, we discuss detailed properties of optical responses found beyond the refraction limit.