Although several noninvasive techniques now exist for vascular imaging, including MR imaging, three-dimensional CT, and color-flow and duplex sonography, the gold standard to which these techniques are compared remains catheter angiography. Cut-film and digital subtraction angiography (DSA) using iodinated contrast material are the standard methods by which vascular imaging is performed. However, despite the development of low-osmolar contrast agents, premedication regimens, and careful patient selection, adverse reactions to contrast material, including idiosyncratic reactions and contrast-induced nephropathy, continue to occur in a small number of patients [1-3]. Carbon dioxide (CO2) was developed as an alternative to iodinated contrast material to avoid these problems [4]. Once the behavior of intravascular gas, the methods of safe delivery, and the principles of successful imaging are understood, the use of CO2 as an intravascular contrast agent during DSA allows accurate imaging with little risk. Recent advances in delivery systems, postprocessing capabilities, and its extension to new vascular interventional procedures have greatly expanded the usefulness of CO2 angiography in both diagnostic and interventional vascular radiology.