Yusuf Khass Hajib (Arabic: يوسف خاصّ حاجب; Yūsuf Khāṣṣ Ḥājib Balasağuni; Turkish: Yusuf Has Hacip; Kyrgyz: Жусуп Баласагын) was an 11th century Uyghur poet from the city of Balasaghun, the capital of the Karakhanid Empire in modern day Kyrgyzstan. He wrote the Kutadgu Bilig and most of what is known about him comes from his own writings in this work.
Balasagun was located near present-day Tokmok in Kyrgyzstan. Yusuf Khas Hajib was about 50 years old when he completed the Kutadgu Bilig. After presenting the completed work to the prince of Kashgar he was awarded the title Khāṣṣ Ḥājib, an honorific similar to "Privy Chamberlain" or "Chancellor".
He is also referred to as Yūsuf Balasaguni.
Some scholars suspect that the prologue to the Kutadgu Bilig, which is much more overtly Islamic than the rest of the text, was not written by Yūsuf, particularly the first prologue, which is in prose, unlike the rest of the text.
Yusuf Khas Hajib died in 1085 at the age of 66 in the city of Kashgar, and was buried there. There is now a mausoleum erected on his gravesite.