Portugal has a weak tradition as far as public policy evaluation is concerned. In tact, the latter arose almost entirely as a response to external demands associated with programmes involving international or European Union funding or legal requirements. In this context, the evolution of evaluation in the field of spatial planning, which is not a formal European Unian competency has followed its own particular course to other public policies far more exposed to normative exogenours factors. In reconstituting the history of this development we can see that over a period of 13 years the aims of evaluation in the field of spatial planning have become increasingly broad, growing from a simple assessment of policy conformity to a preemptive impact assessment and later on to an evaluation of territorial dynamics in spatial planning processes and practices. This widened scope has meant that evaluation in spatial planning is nowadays part of a larger universe of evaluative practices that focus on the territorial nature and impacts of specific public policies. This chapter highlights both the advantages and the tensions of that incorporation, and proceeds to a critical analysis of the purpose of the Territorial Impact Assessement instrument and the conditions this this tool to be adopted in Portugal. Assuming a construtivist approach, the need to transform spatial planning evaluation into a source of policy-learning, institutional innovation and citizenship is stressed as a crucial challenge for the near future both at the European and the domestic level.