A variety of Transparency-Enhancing Technologies has been presented during the past years. However, investigation of frameworks for classification and assessment of Transparency-Enhancing Technologies has lacked behind. The lack of precise classification and categorization approaches poses an obstacle not only to systematic requirements analysis for Transparency-Enhancing Technologies but also to investigation and analysis of their capabilities and their suitability to contribute to privacy protection. This paper addresses this research gap. In particular, it presents a set of categorization parameters for describing the properties and functionality of a Transparency-Enhancing Technology on the one hand, and a categorization of Transparency-Enhancing Technologies on the other hand.