Measurements of the atmospheric mixing ratios of the main anthropogenic greenhouse gases carbon dioxide (CO2) and methane (CH4) allow us to constrain their emissions and removals to and from the atmosphere (i.e. "sources and sinks").  Additionally, measurements of isotopic ratios of these greenhouse gases, such as 13C:12C of CO2 and CH4, 14C:C in CO2, and D:H of CH4 provide extra insight into the processes responsible for the sources and sinks.  Amongh many other atmospheric constituents, NOAA/GML makes measurements of CO2 and CH4 mixing ratios on air samples collected througout the world, providing a detailed picture of the distributions and trends of these gases.  Moreover, in cooperation with partners at the University of Colorado, Boulder measurements of isotope ratios of these gases are made on the same air samples.  We use these measurements in conjunction with models of atmospheric transport to better understand anthropogenic emissions as well as the relationships between changing climate and greenhouse gas sources and sinks.  Opportunities exist to expand and refine existing efforts as well as to exploit rich datasets of measurements of CO2, CH4, their isotopic ratios, and numerous other atmospheric constituents that we measure.