Have you heard the news? On 17 April 2009, the U.S. Environmental Protection Agency (EPA) formally declared carbon dioxide (CO2) and five other heat-trapping gases as pollutants that endanger public health and welfare. This important milestone sets in motion a process that will lead to the regulation of the gases for the first time in the U.S. As a result, we can expect that CO2 capture and storage in the subsurface and monitoring are going to be of major importance in the future. Our industry has already made significant progress with CO2 monitoring, and in this issue of TLE, we have three technical papers that give a good overview of ongoing work.