Extracellular fluid (ECF) volume expansion has traditionally been considered the primary therapeutic intervention to prevent CIN. Correction of volume contraction with ECF expansion is expected to diminish vasoconstrictive responses that contribute to renal ischemia and decrease contact time and concentration of contrast media within the renal tubules. Early clinical studies using historic controls suggested a beneficial role for ECF expansion. Following these studies, volume expansion quickly became the standard of care, although no prospective, randomized, placebo-controlled studies have been conducted to evaluate its efficacy, probably for ethical concerns. Subsequent studies have attempted to delineate the best protocol for prophylactic ECF expansion, but to date, no consensus has been reached due to variability among studies in quality, size, subject selection, and endpoint definition. The limited literature suggests that intravenous volume expansion is superior to oral, that longer courses of parenteral fluid administration are superior to shorter courses, and that isotonic fluids are superior to hypotonic fluids.