Queen Seondeok (Korean: 선덕여왕 Korean pronunciation: [sʌn.dʌk jʌ.waŋ]; Unknown – 20 February [O.S. 17 February] 647; 8th day of the 1st lunar month of the 14th year of Inpyeong [인평 14년 정월 8일; 仁平14年正月8日]) reigned as Queen Regnant of Silla, one of the Three Kingdoms of Korea, from 632 to 647. She was Silla's twenty-seventh ruler, and its first reigning queen. She was the second female sovereign in recorded East Asian history and encouraged a renaissance in thought, literature, and the arts in Silla. In the Samguk sagi, Queen Seondeok was described as "generous, benevolent, wise, and smart". According to the Legend of Jigwi [ko], she was also beautiful. She developed Buddhist culture, selected great talent, and established diplomacy with the Tang dynasty, laying the foundation for the unification of the Three Kingdoms of Korea. Queen Seondeok is known as a wise and kind monarch, making her one of the most prominent monarchs in Korean history.

In texts, Queen Seondeok is indicated not only as Seondeok yeowang (선덕여왕; 善德女王), but also as Seondeok wang (선덕왕; 善德王), Seondeok yeodaewang (선덕여대왕; 善德女大王) and Seongjohwanggo (성조황고; 聖祖皇姑).

Born Princess Deokman (德曼), Seondeok was the daughter of King Jinpyeong and Queen Maya of Silla. She had two siblings, Princess Cheonmyeong and Princess Seonhwa (although Seonhwa's existence is controversial due to the discovery of evidence in 2009 that points to King Uija's mother as being Queen Sataek and not Seonhwa as indicated by historical records). It is uncertain whether she or Cheonmyeong was the first born. According to the disputed text Hwarang Segi, Cheonmyeong was older than Seondeok. According to the historical text Samguk sagi, Seondeok was the eldest daughter.

According to the disputed text Hwarang Segi, because King Jinpyeong had no son whom he could pass the crown to, he began to consider his son-in-law, Kim Yongsu (husband of Princess Cheonmyeong) as his successor - after recognizing his achievements for the country. When Princess Deokman heard of it, she made a plea to her father, asking him to give her a chance to compete for the throne, insisting that she too had the right to compete for the throne as much as Kim Yongsu had. Seeing her determination, the King gave her the chance to prove herself worthy of the throne. Although it was not unusual for women to wield power in Silla (Queen Sado also served as a regent for King Jinpyeong), the thought of having a female ruler sitting on the throne was still unacceptable for most of them. Therefore, Princess Deokman had to prove herself in order to gain the trust and support of her people. Eventually, she succeeded, and was named as King Jinpyeong's successor. But this story is not mentioned in the historical texts Samguk sagi and Samguk yusa. According to the Samguk yusa, the reason Seondeok became a female monarch was just because there was no male Seonggol of Bone-rank system.

The decision was not accepted by everyone, and as a result; some officials planned an uprising in order to stop her from being crowned. On May of 631, Ichan Chilsuk (이찬 칠숙) and Achan Seokpum (아찬 석품) planned a rebellion. But, their plan was discovered and suppressed early on. As punishment, Chilsuk was beheaded in the market place along with his entire family. Seokpum was able to escape and ran to the Baekje border. However, he missed his wife and decided to return after exchanging clothes with a woodcutter. Upon his return, he was arrested by soldiers waiting for him at his home, and was later executed.

In January 632, Queen Seondeok became the first queen regnant of Silla. As a ruler, Queen Seondeok's primary concern was the livelihood of her people. Right after she was crowned, she appeased her people by telling them what her policies would be. She sent royal inspectors throughout the kingdom to improve the care of widows, widowers, orphans, the poor, and the elderly. During that same year, she sent a diplomat to pay tribute to the Emperor of the Tang dynasty of China, and inform him about Silla's new ruler. However, Emperor Taizong of Tang refused to acknowledge Seondeok as a ruler because she was a woman.

In the second year of Queen Seondeok's reign, Cheomseongdae, an astronomical observatory, was built to help the farmers. She also announced a whole year of tax exemption for the peasants and reduced the tax for the middle class, and through this act of kindness, the queen won the people's support and her position was strengthened against the opposition of the male aristocracy. In June of the same year, Queen Seondeok sent a diplomat to pay nominal tribute to the Tang Emperor again; however, Emperor Taizong still refused to acknowledge her as a ruler but Seondeok was unfazed as Korean rulers of Korean dynasties have always seen themselves as equal to the rulers of Chinese dynasties.

According to the Samguk sagi, in March, 636, the queen became ill and no amount of prayers and medicine worked. In March, 638, a large stone on the south side of the mountain moved on its own, and seven months later, Goguryeo attacked the mountain valley. The next year, the sea water on the eastern part of the Silla kingdom turned red, which caused all of the fish living in it to die. These events made the people anxious, and some of them considered them as bad omens portending the Silla kingdom's downfall.