In this chapter, two subfamilies of atypical cadherins are described: the subfamily of seven-pass transmembrane cadherins (7-TM cadherins) and Fat and Dachsous cadherins. Pioneering genetic studies in Drosophila have defined both subfamilies and dissected their roles in animal development. It is now clear that the founding members in Drosophila and their respective vertebrate homologues make critical and essential contributions to a variety of dynamic behaviors of cell populations, and that malfunctions of those atypical cadherins cause anomalies in embryonic development, resulting in postnatal organ malformation or embryonic demise. Here we discuss how the atypical cadherins control cell behaviors with the emphasis on one particular orchestration of cells along the axes of tissues, organs, or bodies, inclusively designated as planar cell polarity (PCP). Nowadays the purview of PCP ranges from the unidirectional orientation of subcellular structures, such as wing hairs of Drosophila and vertebrate motile cilia, to three-dimensional dynamics of multicellular units, such as tilting hair follicles, neural tube closure, epithelial folding in the oviduct, and collective cell migration. The PCP field is at an extraordinarily exciting juncture, bursting with questions about functions of 7-TM cadherins and Fat and Dachsous cadherins at the cellular and molecular level.