In many areas of non-photorealistic and illustrative rendering, considerable progress has been made toward synthesizing traditional artistic and illustrative techniques. However, evaluation and validation of such images have only been attempted relatively recently. This chapter surveys evaluation approaches that have been applied successfully in non-photorealistic and illustrative rendering. It provides an overview over different evaluation approaches including qualitative and quantitative techniques and gives examples for how to approach evaluation in the NPR context. Collectively, the described techniques do not only answer the question of whether an NPR technique is able to replicate a traditional technique successfully but also what implications the use of NPR techniques has and what people think about different NPR techniques as compared to traditional depictions.