Simultaneous interpretation has generally been regarded as a process involving spoken languages. Either the source language or the target language, however, may be a natural sign language. In this paper, sign language interpretation is defined within a semiotic framework of the broader field of translation. Psycholinguistic studies of sign language interpretation are reviewed in the areas of time lag, probability prediction, error analysis, and memory. Semiotic and psycholinguistic models of sign language interpretation are presented.