The assessment of regional lung function to predict postoperative function is integral to preoperative evaluation of pulmonary resection candidates who have impaired lung function. The four validated ways are: anatomic calculation, split radionucleotide perfusion scanning with single photon emission CT (SPECT), quantitative CT scanning, and dynamic perfusion MRI. Estimations of PPO lung function based on anatomical calculations are the simplest, tend to overestimate postresectional functional loss, and should be performed in most operative candidates. Patients requiring further evaluation require one of the other techniques: SPECT, quantitative CT, or MRI. All effectively predict postoperative forced expiratory volume in 1 second (FEV₁). Cost, local expertise and availability, and the need to predict postoperative maximum oxygen consumption (VO₂ max) dictate the clinician’s choice.