This paper presents a study of modality in Iranian Sign Language (ZEI) from a cognitive perspective, aimed at analyzing two linguistic channels: facial and manual. While facial markers and their grammatical functions have been studied in some sign languages, we have few detailed analyses of the facial channel in comparison with the manual channel in conveying modal concepts. This study focuses on the interaction between manual and facial markers. A description of manual modal signs is offered. Three facial markers and (...) their modality values are also examined: squinted eyes, brow furrow, and downward movement of lip corners (horseshoe mouth). In addition to offering this first descriptive analysis of modality in ZEI, this paper also applies the Cognitive Grammar model of modality, the Control Cycle, and the Reality Model, classifying modals into two kinds, effective and epistemic. It is suggested that effective control, including effective modality, tends to be expressed on the hands, while facial markers play an important role in marking epistemic assessment, one manifestation of which is epistemic modality. ZEI, like some other sign languages, exhibits an asymmetry between the number of manual signs and facial markers expressing epistemic modality: while the face can be active in the expression of effective modality, it is commonly the only means of expressing epistemic modality. By positing an epistemic core in effective modality, Cognitive Grammar provides a theoretical basis for these findings. (shrink)