Wearable or implantable devices would potentially allow patients to benefit from longer treatment durations with greater solute clearance and improved volume balance. However, wearable devices also have to maintain electrolyte and acid-base homeostasis. Although several groups have developed wearable devices on the basis of peritoneal dialysis with regeneration of spent dialysate using carbon and other sorbents, definitive clinical trials remain awaited. The development of a truly wearable hemodialysis device has been a goal since 1970s, and despite many attempts there has only been one recent “proof-of-concept” clinical trial, which showed that such a device would be predicted to achieve greater small- and middle-sized, water soluble solute and protein bound toxin clearance compared with the standard three-times-a-week conventional hemodialysis. However, many hurdles have to be overcome before a proof-of-concept device can be brought to clinical practice.