Evidentiality refers to the linguistic encoding of how information about an event is known. Korean is among the languages that express source information using grammatical particles. To date, Korean linguists have primarily focused on regulating the grammaticality of this phenomenon. In this chapter, we report existing findings that provide psychological evidence of how Korean users process source information during both production and comprehension. Our results indicate that Korean evidential markers are used optionally, appearing in approximately 30% of instances, with the hearsay source being marked more frequently than the direct perceptual source. This preference for hearsay was also observed in the judgment of verb agreements based on evidential cues during online sentence comprehension. Of interest, the neutral/unmarked marker often took on epistemic overtones, resulting in a visual interpretation in both production and comprehension.