The carbon benefits from forest bioenergy have been controversial with some environmental groups and scientists considering it to be even worse than coal while others contend that its use can lead to substantial savings in emissions relative to coal. Studies assessing the GHG implications of forest bioenergy differ in the source of emissions (biogenic or life-cycle) that they are accounting for, the metric used for this accounting, the spatial scale at which these emissions are measured, the time frame over which they are measured, and the counter-factual baseline to which emissions with the use of forest bioenergy are compared. This paper discusses the implications of these underlying differences. It shows that the spatial and temporal scales for assessment, and the extent to which market feedback effects and behavioral responses are incorporated, play a critical role in the widely different assessments obtained by these studies.