The talk will be divided in two parts. The first part will be devoted to diffraction tomography based on the scalar wave equation to obtain images of the refractive-index distribution of an object embedded in a homogeneous medium, with emphasis on experimental verifications of this technique in applications using light or ultrasound. The second part of the talk will be devoted to imaging of objects embedded in turbid media, based on radiative transfer theory. Here the emphasis will be on passive optical remote sensing from satellite for identifying and mapping algae distributions in the ocean, as well as on the use of light for diagnosis of skin abnormalities, such as skin cancer.