How should Australian criminal trial courts treat evidence deriving from illegally or improperly obtained evidence? The fact that derivative evidence gives rise to factors distinct from primary evidence makes it deserving of an examination of its peculiarities. In doing so, the assumption may be put aside that derivative evidence falls wholly within the established general discourse of illegally or improperly obtained evidence. Just as the judicial response to primary evidence must be intellectually rigorous, disciplined and principled, so must be the response to derivative evidence. As such, a principled analysis of how Australian courts should approach derivative evidence can significantly contribute to the discourse on the law with respect to the exclusion of illegally or improperly obtained evidence. This thesis provides that principled analysis by arguing that the principles which underpin and inform the discretionary exclusionary frameworks within Australia require an approach which is consistent as between illegally obtained derivative evidence and illegally obtained primary evidence.