Recently, new approaches for miniaturization and transportability of medical devices have been developed, paving the way for wearability and the possibility of implantation, for renal replacement therapies. A wearable artificial kidney (WAK) is a medical device that supports renal function during ambulation or social activities out of hospital. With the aim of improving dialysis patients' quality of life, WAK systems have been developed for several decades. However, at present there are a lot of technical issues confronting the attempt to apply WAK systems in clinical practice. This article focuses on technical requirements and potential solutions for WAKs and reviews up-to-date approaches related to dialysis membrane, dialysate regeneration, vascular access, patient-monitoring systems and power sources for WAKs.