Linguistic evaluation has become an important area of inquiry in recent years. In the traditions of, e.g., lexical semantics, phraseology, corpus linguistics, and interactional linguistics, a large inventory of linguistic means have been identified by which speakers can express evaluative meanings. However, the class of German sentential idioms, e.g., Das kannst du dir in die Haare schmieren (lit. 'You can smear that into your hair', fig. 'That is useless'), has not gained much attention. This paper explores how the evaluative meaning of German sentential idioms is constructed syntactically, semantically, and pragmatically. In particular, it is investigated how the meaning of these idioms interacts with the context in which they are used. A context model of evaluation is developed in which the cognitive category of cause plays a central role. The model is applied to contextualized examples, the findings supporting the hypothesis that cause is one of the core categories of evaluation.