This chapter discusses self-organization and its effects in optics. One of the most exciting and potentially useful areas of current research in optics involves the understanding and exploitation of self-organization in nonlinear optical systems. This self-organization may sometimes lead to the evolution of complex spatial patterns that can be regarded as the nonlinear eigenmodes of the system. Generation of these patterns is characteristically marked by the presence of intensity thresholds. In a nonlinear system with complicated temporal dynamics, it turns out that one cannot retain purity in spatial dimensionality. It is therefore equally important to investigate the dynamics of the transverse spatial variations, which in fact give rise to very interesting patterns due to self-organization. A vast wealth of patterns can be achieved by using a nonlinear optical element with feedback that has the capability of providing field transformation, for example, by spatial filtering. These types of systems are called optical kaleidoscopes simply because of the different self-organized patterns that they can generate.