Intra-abdominal pressure (IAP) measurements are essential to the diagnosis and management of intra-abdominal hypertension (IAH) and abdominal compartment syndrome. A variety of IAP measurement techniques have been described. The intravesicular or "bladder" technique remains the gold standard. This commentary reviews each of the different techniques for IAP measurement and discusses their clinical application. It also explores how IAP is affected by changes in body position, body mass index, and positive end-expiratory pressure (PEEP). IAP should be measured every 4 to 6 hours in patients with risk factors for IAH. Putting patients in the semirecumbent position changes the IAP measurement significantly. The role of prone positioning in unstable patients with IAH remains unclear. PEEP has a small effect on IAP.