Accurately simulating feedbacks among meteorology, chemistry, aerosols, clouds, and radiation requires fully-coupled online climate and chemistry models and presents significant challenges in terms of both scientific understanding and computational demand. A unified global-through-urban fully-coupled model will provide a state of the science model framework to study such feedbacks with consistent model physics for applications on all scales. As the first step toward a unified Global-through-Urban Weather Research and Forecast Model with Chemistry (GU-WRF/Chem), we will develop a global WRF/Chem and test it with an existing testbed based on the mesoscale WRF/Chem from NOAA and newly-developed global WRF from NCAR. Our ultimate objective is to apply GU-WRF/Chem to replicate and examine feedbacks among multiple components through multiple processes in one atmosphere and to reduce uncertainties associated with current climate-chemistry modeling at regional and global scales. Recommendations for future model development for both global WRF and global WRF/Chem will be provided based on initial development, preliminary testing, and lessons learned from this work.