This dissertation probes the development of written culture on the Korean peninsula and in the Japanese archipelago in the early historic period, roughly the sixth through eighth centuries CE, through the study of archaeologically excavated wooden documents known as mokkan木簡. In particular, this study aims to understand the various functions of writing in early historic Paekche (trad. 18BCE-660CE), Silla (trad. 57BCE-935CE), and Japan, and explore how literary writing first emerged in these contexts. In addition to being used for bureaucratic documentation, record-keeping, and ritual purposes, because of the unique material characteristics of wood, mokkan played an important role as surfaces for literacy acquisition, composition practice, and the drafting of documents. As a result, they are both a window into emergent written culture overall and a particularly rich archive for the study of emergent literary approaches to writing. Mokkan are contextualized alongside other extant materials, such as stone inscriptions and documentary sources from later periods. The goals of this dissertation are two-fold: one is fundamentally comparative, seeking to illuminate how mokkan unearthed from sites on the Korean peninsula and the Japanese archipelago can help to flesh out our understanding of the development of written cultures throughout the region. The other goal is to highlight the connections between these written cultures and make the case that these did not develop in isolation from each other. Because of the frequent movement of people among Paekche, Silla, and Japan both prior to and during the early historic period, and particularly because of the exodus of literate Paekche elites into Japan that occurred in the aftermath of the Battle of the Paek River, this dissertation argues that an understanding of the connections among the written cultures of these three kingdoms is essential to understanding the written culture of any one of them. This dissertation is organized into four chapters. Chapter 1 treats the history of writing and the development of written culture in the kingdom of Paekche on the Korean peninsula through mokkan. The chapter makes particular note of nascent literary tendencies seen among the Paekche mokkan corpus and how these might inform our understanding of written culture in Japan, where many Paekche refugees fled after the Japanese navy’s defeat at the Battle of the Paek River in 663. Chapter 2 contrasts the development of written culture in pre-unification Silla (trad. 57BCE-668CE) with that of Paekche, highlighting the unique speed with which written culture expands in mid-sixth century Silla during the reign of King Chinhǔng through an examination of both monumental inscriptions on stone steles and more mundane inscriptions found on mokkan from sites in both the provinces and the royal capital. In addition, the chapter probes in detail evidence for early vernacularization in Silla as observed through pieces of correspondence inscribed on mokkan, but notes that examples of nascent literary writing are few. Chapter 3 evaluates the evidence for the emergence of written culture at Japan’s mid-seventh century courts in Naniwa (645-652) and Ōmi (667-672), in the context of evidence from the peninsula. In particular, the chapter takes up the narrative of the preface to Kaifūso (751) as a frame for interpreting the evidence for literate communities and literary writing at these two palace sites, and centers the role of Paekche refugees in the post-Paek River defeat modernization efforts carried out by the sovereign Tenchi (r. 661-672). Chapter 4 examines the emergence of a mature written culture in Japan through extant mokkan from the late seventh century capitals at Asuka and Fujiwara, connecting them to the intensified modernization programs under Tenmu (r.672-686) and Jitō (r. 686-797). This chapter presents evidence for the composition of literary writing in both Literary Sinitic and the vernacular, and argues that these forms were probably more or less equally important. Finally, the Conclusion connects the sixth and seventh century evidence presented in Chapters 1-4 to the elements of the literary cultures of the eighth century in both Korea and Japan.