The Kamianets-Podilskyi Castle (Ukrainian: Кам'янець-Подільська фортеця, romanized: Kamianets-Podilska fortetsia; Polish: twierdza w Kamieńcu Podolskim; Lithuanian: Podolės Kameneco tvirtovė) is a former Ruthenian-Lithuanian castle and a later three-part Polish fortress located in the historic city of Kamianets-Podilskyi, Ukraine, in the historic region of Podilia in the western part of the country. Its name is attributed to the root word 'kamin', from the Slavic word for 'stone'.

Historical accounts date Kamianets-Podilskyi Castle to the early 14th century, although recent archaeological evidence has proved human existence in the area back to the 12th or 13th century. Initially built to protect the bridge connecting the city with the mainland, the castle sits on top of a peninsula carved out by the winding Smotrych River, forming a natural defense system for Kamianets-Podilskyi's historic Old Town neighborhood.

Its location on a strategic transport crossroad in Podilia made the castle a prime target for foreign invaders, who rebuilt the castle to suit their own needs, adding to its multicultural architectural diversity. Specifically, the complex consists of the Old Town fortified by King Casimir IV, the Old Castle rebuilt by Kings Sigismund I and Stephen Báthory, and the New Castle founded by Kings Sigismund III and Władysław IV. However, in spite of the many architectural and engineering changes to the original structure, the castle still forms a coherent architectural design, being one of the few medieval constructions in modern-day Ukraine that is relatively well preserved.

Along with the Old Town neighborhood, the castle is listed as part of the National Historical-Architectural Reserve "Kamianets" and the National Environmental Park "Podilski Tovtry". The complex is a candidate UNESCO World Heritage Site, nominated in 1989 by the Ukrainian representatives, and also one of the Seven Wonders of Ukraine. Today, Kamianets-Podilskyi Castle is the most recognized landmark of the city, serving as an important regional and national tourist attraction.

Traditionally, Kamianets-Podilskyi Castle was thought to have been founded during the second half of the 14th century, as the first accurate historical accounts of the castle date back to the mid-14th century, when most of the territories of western Rus' were under control of the Grand Duchy of Lithuania. A written document by Prince Yuriy Koriatovych in 1374, for example, mentions that the Magdeburg rights would be presented to Kamianets inside the castle. Archaeological excavations during the 1960s, however, provided contrasting evidence suggesting that the castle might date back even earlier to the end of the 12th or the beginning of the 13th centuries. It is also clear from historical and archaeological evidence that an earthen fortress existed in the area during the time of the East Slavic state of Kievan Rus', but not on the same site as the current castle.

The castle was outdated but remained vital to the defense of Kamianets and nearby trade routes; as a result, the voivode of Kraków, Spytek of Melsztyn, began modernizing the complex at the turn of the 15th century. During the reconstruction, the old towers were renovated and ten new towers were added. A century and a half later, the castle was updated again, this time by military engineer and architect Hiob Bretfus, who built the New Western and Eastern Towers, the castle's eastern wall and an underground gallery, as well as the Full Gates and housing for the town's starosta community.

During the mid-14th to mid-15th centuries, Kamianets-Podilskyi Castle was located on one of the main frontiers of the Polish–Lithuanian Commonwealth. From 1434 until its annexation by the Russian Empire in 1793, the castle played a major role in the defense against the oncoming Cossack, Ottoman, and Tatar invasions; from the 15th through 17th centuries, the castle was attacked by Tatar hordes a total of 51 times. The Tatar invasions of 1448, 1451, 1509, and 1528, as well as the Ottoman siege of 1533, caused damage to both the castle and the city but all of these invasions were successfully repelled.

Kamianets-Podilskyi Castle played an important role during the Khmelnytsky Uprising between 1648 and 1654, when the Zaporozhian Cossacks led by Hetman Bohdan Khmelnytsky, allied themselves with the Crimean Tatars and the local Ukrainian peasantry against the Polish–Lithuanian Commonwealth's army and militia. During the uprising, the castle was unsuccessfully besieged by local Cossacks and insurgents led by Commander Maksym Kryvonis. In 1651, the castle was then subject to another Cossack siege led by Hetman Ivan Bohun, before an unexpected counterattack by Polish insurgents under commanders Aleksandrenka and Chuika re-established the Polish presence in the area and relieved the siege. A 60,000 force army led by Khmelnytsky himself reasserted Cossack control over the castle in 1652. Just one year later, the castle was attacked yet again, this time by a 40,000 strong Crimean Tatar horde.