The Biological Condition Gradient (BCG) is a conceptual scientific model that describes biological conditions along a gradient of six levels from natural biological integrity to severely altered conditions in response to increasing levels of stressors.  The BCG should be used to provide greater transparency in how reference conditions are developed and compared from one program or region to another as well as how assessment decisions are made in those programs.  Greater application of the BCG is occurring in biological assessment programs using a wide array of approaches from expert consensus to statistical modeling.  The six levels of the BCG are not intended as predetermined benchmarks or thresholds describing acceptable or unacceptable conditions but as a conceptual tool to better inform the development and establishment of reference conditions and assessment decisions. This special session is intended to provide a forum to share ideas and approaches on how the BCG can be successfully applied in biological assessment programs.