Fluid management in critical illness has undergone extensive reevaluation in the past decade. Since a significant percentage of critically ill patients develop acute kidney injury (AKI), optimal fluid management is even more paramount to prevent the ill effects of either underhydration or overhydration. The concepts of early goal-directed fluid therapy (EGDT) and conservative late fluid management permeate current clinical research, and the independent association between fluid accumulation and mortality has been repeatedly demonstrated. A number of prospective randomized trials are planned to provide an adequately powered assessment of the effect of EGDT or earlier renal replacement therapy initiation in patients with, or at risk for AKI. The aim of this analytical review is to use existing clinical and physiological studies to support a 3-phase model of fluid management in the critically ill patient with AKI.