The Continual Intercomparison of Radiation Codes (CIRC) aims to evaluate the radiation codes of Global Climate Models (GCMs) with line-by-line reference calculations operating on cloudless and cloudy atmospheric profiles observed by the Atmospheric Radiation Measurement Program (ARM). CIRC is supported by ARM and endorsed by the GEWEX Radiation Panel and the International Radiation Commission. A key feature of the intercomparison is that its reference calculations are validated with ARM spectral and broadband radiation measurements. A brief description of the first phase of the project provides the opportunity to highlight important issues that need to be addressed in order to improve GCM radiative transfer for current and future climate conditions.