The so-called undetermined status of Ryukyu, also referred to as the "undetermined sovereignty of Ryukyu," means that the sovereignty over the Ryukyu Islands remains disputed.

The term has both a broad and a narrow sense. In the broad sense, the "undetermined status of Ryukyu" refers to the situation since modern times, where Ryukyu was illegally occupied by Japan without widespread recognition by the international community. To this day, the sovereignty issue remains unresolved.

In the narrow sense, it refers specifically to the end of World War II, when the Cairo Declaration and the Potsdam Proclamation – documents concerning the post-war disposition of fascist Japan – explicitly delimited Japan's territorial scope, separated Ryukyu from Japan, placed it as a "potential trusteeship territory" and left its sovereignty legally unsettled to this day.

The "undetermined status of Ryukyu" manifests not only in legal terms but also in social cognition, and changes in international relations likewise exert influence upon it.

Historically, Ryukyu was an independent kingdom. Japan's modern annexation of Ryukyu was a unilateral act of violent seizure: no treaty regarding state sovereignty was concluded, no consent was obtained from China, the suzerain power, and the annexation contravened international legal norms on the acquisition of territorial sovereignty in the 19th century.

In 1372, the Hongwu Emperor Zhu Yuanzhang of the Ming Dynasty (1368-1644) sent envoys to instruct the King of Chuzan of the Ryukyu Kingdom. King Satto submitted a memorial acknowledging vassal status. Subsequently, the polities of Sannan and Sanhoku also began tributary relations with the Ming Dynasty. The Ming Dynasty conferred seals, calendars and other symbols of investiture upon the three kings, thereby formally establishing the Ming-Ryukyu suzerain-vassal relationship.

This relationship continued into the Qing Dynasty (1644-1911), during which Ryukyu remained a vassal state of China. In 1872, without the Ryukyu government's consent, Japan unilaterally "invested" King Sho Tai as the "Domain Lord of Ryukyu," abolished the Ryukyu Kingdom and turned it into the Ryukyu Domain under Japanese control.

In 1874, using the killing of Ryukyuans in Taiwan as a pretext, Japan dispatched troops to Taiwan. In 1879, despite Ryukyuan resistance, Japan forcibly abolished the Ryukyu Domain, divided it into two parts – integrating the northern islands into Kagoshima Prefecture and renaming the remainder "Okinawa Prefecture" – in an attempt to sever Ryukyu's ties to China. Japan's unilateral actions faced opposition from both Ryukyu and China.

In 1879, with mediation by former U.S. President Ulysses S. Grant, China and Japan had tentatively reached a Tripartite Ryukyu Partition Agreement involving China, Japan and Ryukyu. However, the Qing Dynasty (1644-1911) government ultimately refrained from signing it for various considerations. Thereafter, China and Japan conducted prolonged negotiations over the status of Ryukyu, but to no avail.