The pattern of linearly polarized light in the sky can be used for orientation behavior by many insects. Although such behavioral responses have been well described in bees and ants over several decades, until recently it remained largely elusive how polarized-light information is processed in the insect brain. However, over the last decade, substantial advances in understanding polarizedlight processing have been made, based on behavioral, electrophysiological, and anatomical data. Particularly, progress was made in the desert locust, but based on comparative work in the field cricket, the monarch butterfly, and the fruit fly broader conclusions about how polarized-light information is encoded in the insect brain in general begin to emerge. After polarized light is detected by photoreceptors of specialized parts of the compound eye, this information passes through the optic lobe, the anterior optic tubercle, and the central complex. In these brain regions, detailed neural responses to polarized light have been characterized in a large set of anatomically defined neurons that together comprise the polarization vision network. This work has begun to unravel how polarized light is integrated with unpolarized light, and how response characteristics of involved neurons are modulated in context-dependent ways. Eventually, all skylight cues appear to be combined to generate a neural representation of azimuthal space around the animal in the central complex of the brain, which could be used as a basis for directed behavior. Polarized-light information is likely contributing to such a representation in many insects and thus this modality could be crucial for illuminating how the insect brain in general encodes the position of the animal in space, a task that all animal brains have to master. 61 62 S. Heinze therefore POL1 neurons could act as three analyzer channels, was strong support for the hypothesis of instantaneous E-vector detection. A decade later, it was shown by work from the laboratory of Uwe Homberg that the cricket was not the only species in which polarization-sensitive neurons could be analyzed (Homberg and Würden 1997;Vitzthum et al. 2002). In the desert locust (Schistocerca gregaria), several types of neurons were described that also responded to changes in E-vector orientation. Most of these cells were located in the center of the brain in a region called the central complex. It therefore became evident that the complexity of the neural network involved in processing of polarized light was substantial, and much effort was since put into the task of describing additional neural elements that together constitute the polarization vision network of the insect brain.The main scope of this chapter is to summarize the work over the last decade that immensely widened our knowledge about how polarized light is processed in the brain of insects, particularly in the desert locust, but also in the cricket, in the monarch butterfly (Danaus plexippus), and-very recently-in the fruit fly Drosophila melanogaster. The e...