Joseon missions to Japan (Ko. Joseon:Tongsinsa) were goodwill missions sent intermittently by Joseon Dynasty Korea at the request of the Japanese bakufu authorities. During the Edo period, these missions were dispatched to the Tokugawa shogunate 12 times between 1607 and 1811. The Joseon Dynasty was during this period a vassal state of Ming China before 1637, and then of Qing China after 1637. In consideration of the early-modern diplomatic principle in East Asia that "the minister of a prince had no intercourse outside his own state" (Ch. Ren chen zhe wu wai jiao 人臣者無外交), the Joseon Dynasty, as a vassal state, should have been prohibited from building any diplomatic relationship with Tokugawa Japan without the permission of the suzerain. Nonetheless, there has been little research on the whether and how the suzerain-vassal relationship between Ming and Qing China and Joseon Korea impacted the relationship between Joseon Korea and Japan, not to mention the impact on Joseon missions to Japan, which was a crucial representation of the good-neighborly relationship. By paying close attention to suzerain-vassal relationships, issues concerning the Joseon missions to Japan may be examined more comprehensively. In this article, I use the Waejeong Jamun (Ch. Woqing Ziwen 倭情咨文), official reports on the Japanese political situation that were sent by the Joseon dynasty to Ming and Qing China, as a case study to offer a solution to this problem. The Waejeong Jamun have previously been seen as an effective tool for addressing the issue of Joseon Korea's relations with Qing China, and of great significance on Qing China's policy and attitude toward Tokugawa Japan. Among the Waejeong Jamun are some on the preparation, dispatching, and debriefing of Joseon missions to Japan that contain vital clues. After decoding the reports related to the Joseon missions to Japan, it is clear that in making the decision to dispatch missions to Japan from 1636 to 1811, Joseon Dynasty officially asked for Qing China's permission. However, in actuality, the Joseon Dynasty independently made the decision to send missions after 1655. As for the dispatching of Hoedam-gyeom-swaehwansa (Jp. Kaito-ken-sakkanshi 回答兼刷還使) from 1607 to 1624, the Joseon Dynasty officially sought Ming's approval for the dispatch of missions to Japan; however, in reality they began all the preparations and even sent delegations prior to sending the report to Ming China, which indicates that the report had gradually become a mere formality. For the Joseon mission to Japan in 1643, the dispatch was decided according to the will of Qing Emperor Hong Taiji. By deciphering three reports relating to the 1643 mission, we can see the consistency of Hong Taiji's deep concerns about Japan during his reign. Hong Taiji not only showed strong interest in Japan, i.e. an intention of trading with Japan, which appeared in Namhansanseong Treaty 南漢山詔諭 in 1637 as a post-war settlement of the Second Manchu invasion of Korea, but also sent ministers to the Korean House in Mukden 瀋館 to collect intelligence on the Japanese. Moreover, Hong Taiji intended to utilize Joseon missions to Japan as a channel to collect Japanese intelligence, so he paid special attention to the 1643 mission and intervened directly in its dispatch. The Joseon mission to Japan in 1643 has been regarded as exceptional because it was dispatched for the birth of the young prince 若君, instead of the succession of a new shogun, which was the reason for the dispatch of other Joseon missions to Japan. Thus at first, the Joseon Dynasty passively dispatched missions upon Japanese request; later, the suggestion of Choe Myeonggil 崔鳴吉 is considered the main reason for the positive change in the Joseon court's attitude towards the missions, as Nakao Hiroshi has pointed out However, this article envisions the significant role played by Qing China as the promoter of the Joseon Dynasty's missions, particularly the 1643 mission, and thus how this mission e