Rare kidney diseases are a unique subset of renal disorders that are often termed ‘orphan’ as a result of a multitude of reasons: the small number of patients with the consequent lack of well-defined natural history and course of many of these diseases, limited awareness among the medical community, and finally the significant cost of developing novel therapeutics which makes many of these diseases unattractive targets for the pharmaceutical industry. Nevertheless, in the last decade the study and clinical management of rare kidney disease patients has been the focus of many investigative efforts. In recent years we have witnessed an enormous expansion in our knowledge of the genetic nature of a number of rare kidney diseases. Moreover, the investigation of the role of genetic disruption aiming at elucidating the pathogenesis of different and complex renal diseases has helped not only in understanding the disease states, but has also given us fundamental insights into a number of kidney developmental and physiological functions. This article will give an overview of orphan renal diseases with particular emphasis on monogenic kidney diseases. It will also focus on the classification of these diseases while highlighting a prominent example in each category.