Renal replacement therapy (RRT) is an important therapeutic and supportive measure for acute kidney injury (AKI) in the critical care setting. While RRT is extensively used in clinical practice, there remains uncertainty about the ideal circumstances of when to initiate RRT and for what indications. Many factors, including logistics, resource availability, physician experience and patient-related factors are involved in the decision of when to start and stop RRT for those with AKI. Among the patient-related factors, examples include 'dynamic' trends in AKI and/or non-kidney organ dysfunction, additional measures of acute physiology, such as fluid accumulation and relative oliguria. There currently exists a large variation in clinical practice regarding starting and stopping RRT, due in part to the lack of consensus on this issue. In this article, we briefly review a new opinion-based algorithm to aid in the decision on when to initiate RRT in adult critically ill patients. This algorithm was developed using available clinical evidence, recognizing the inherent limitations of observational studies. It aims to provide a starting point for clinicians and future prospective studies. We also review the available literature on discontinuation of RRT and propose a few simple recommendations on how to 'wean' patients from RRT.