The ways in which oxygen (O2) and carbon dioxide (CO2) are carried in the blood are well known and well understood, with a plethora of textbooks, both general and lung specific, all presenting the topic in a very similar manner. This first of two companion chapters similarly summarizes this information. First, carriage of gases by physical solution is described, followed by discussion of O2, carbon monoxide, and CO2 transport in that order. However, what available texts have not emphasized is why knowing how gases are carried in blood matters, and the second, companion, chapter specifically addresses that critical aspect of gas exchange physiology. In fact, each of the chapters in this volume describes physiological behavior that depends more or less directly on the dissociation curves of O2 and CO2.