In recent years, the discovery of peripheral opioid receptors has challenged the dogma of opioids interacting exclusively with the central nervous system. In this article, we describe the current understanding of the roles of opioids and opioid receptors in renal physiology and pathophysiology. The renal response to opioid exposure varies depending upon the specific opioid agonist, dose, and duration of exposure. The known acute effects of opioids on the kidney impact salt and water balance. The chronic effects of opioid exposure on kidney function are largely unknown, but collapsing glomerulopathy has been associated with chronic heroin abuse. Opioid exposure can lead to both physiological and architectural renal changes, and this may have important clinical implications. Since opioids are often used for pain management in patients with existing kidney disease, their role in kidney function warrants attention.