Hwandan Gogi (Hangul: 환단고기; Hanja: 桓檀古記), also called Handan Gogi, is a compilation of texts on ancient Korean history. It is a bound volume of four supposedly historical records: Samseonggi, Dangun Segi, Bukbuyeogi and Taebaek Ilsa.
According to its introduction, it was compiled in 1911 by Uncho Gye Yeon-su (운초 계연수, 雲樵 桂延壽; ? – 1920) and supervised by Yi Gi (이기,李沂; 1848 – 1909). However, the only currently known copy is Yi Yu-rip's transcription, restored and published in 1979. The work is widely regarded as a modern forgery.
The four books comprising the Hwandan Gogi are:
- Samseonggi (two volumes), describing ancient kingdoms called Hwan-guk that lasted for 3301 years, and Hwanung's 1565-year rule of Baedalguk.
- Dangun Segi (Hangul: 단군세기; Hanja: 檀君世紀), chronicling the history of Gojoseon with 47 generations of Dangun rulers.
- Bukbuyeogi, describing the six kings of Bukbuyeo (North Buyeo).
- Taebaek Ilsa, describing the histories of Hwan-guk, Baedalguk, Samjoseon, Goguryeo, Balhae, and Goryeo; also includes the text of Cheonbu-gyeong.
Dispute regarding authenticity
- There are words from modern language. (for example, '男女平權; the equality of man and woman', '父權; paternal rights')
- The route through which Hwandangogi was first published is not clear.
- Yi Gi could not have supervised the Hwandangogi which was first compiled in 1911, because he died then.
- The contents of Cheonbu Gyeong could not be included in Taebaek Ilsa before 1911 because the Cheonbu Gyeong was first discovered and known to the Daejonggyo in 1916 by Gae Yeonsu, the person who compiled Hwandan Gogi.
- The 1911 edition (or any edition before 1979) has not been found. There is no proof that the book was kept by Yi Yurip and lost in 1975, and then restored by Yi Yurip before 1979.
Other criticisms made on a South Korean television show include unrealistic descriptions found in the texts, for example:
- Hwan-guk is said to have spanned several thousand kilometers ~10,000 years ago
- Rulers of Baedal are said to have lived regularly for 120–150 years
Some historians view the Hwandan Gogi as worthy of further scholarly scrutiny, believing that it is at least partly based on historically valuable, ancient (if not literally accurate) texts.
- The record that five stars were arranged in straight line at 1733 BCE (오성취루, 五星聚婁). This astronomical record in Hwandan Gogi is proved by Professor Park Changbeom, and it is published in the journal. They show that the five stars were arranged in straight line at 1734 BCE with the assumption that Gojoseon was established at 2333BCE.
- Law Professor Junhwan Go asserts several reasons why the Hwandan Gogi is considerable.
- The territory of Gojoseon described in Hwandan Gogi accords with the distribution area of the mandolin-shaped dagger of Gojoseon. Moreover, this territory as advocated by Yoon et al. and Yi Byeongdo coincides with the territory described in Hwandan Gogi.
- 엠파스 한국학 지식 - 한국의 인물 - 이 기(李沂)
- History Special: The Handan Chronicle, KBS 1999
- Am-Ro Ahn ed., Handan Gogi
- 박창범, 라대일, "단군조선시대 천문현상기록의 과학적 검증 (Scientific proof of astronomical record in Gojoseon), 한국상고사학보, vol 14
- Hwandan Gogi explains why the Mausoleum of Dangun is located at in Kangdong near Pyongyang, North Korea - 고준환, "단군신화설은 식민사학자들의 왜곡.농간", (경기대 법학과 교수), 개천절에 되새겨 보는 '실증적' 단군조선사, 오마이뉴스, 2003-10-03 13:15 조인성(경희대 사학과 교수). It states that the fifth Dangun Gueul died while travelling the south area of Gojoseon, and then he has been buried at Daebaksan. The Daebaksan is located at current Pyongyang.
- Hwandan Gogi explained that the era name of Mun wang of Balhae was Daeheung (대흥, 大興) before the era name of Mun wang was discovered in the tombstone of princess Jeonghyo (정효공주묘비, 貞孝公主墓碑) in 1980 - Retrieved from Empas Korean Information  엠파스 한국학 지식
- Hwandan Gogi states that era name of Jangsu Taewang of Goguryeo was Geonheung (건흥, 建興). This era name is used in a Buddhist statue in Chungju of Chungbuk. Before Hwandangogi was published, the statue was considered to be from Baekje - 고준환, 신명나는 한국사, 인간과자연사 (2005) ISBN 8987944433
- 윤내현, 박선희, 하문식, 고조선의 강역을 밝힌다 (The Territory of Gojoseon) (2006) ISBN 8942310893
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- 계연수(이유립 복원본), 환단고기, 한뿌리 출판사, 2005
- 『환단고기(桓檀古記)』에 대한 새로운 이해』, Land Portal
- 정영훈(The Academy of Korean Studies 한국학중앙연구원), '환단고기' 토대로 상고사 연구 보류해야 - 검증안 된 내용 왜곡 우려, The Cheju National University Press 제주대 신문, 2004-03-31
- 김정배, 한국사 권4 - 초기국가 – 고조선.부여.삼한, National Institute of Korean History 국사편찬위원회, 1997. pp. 53
- 안창범(제주대 명예교수),  桓檀古記 僞書論 批判, 한국종교사연구 통권 제10호 (2002. 2)
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- 金庠基, 李海鶴의 生涯와 思想에 대하여, 李瑄根華甲紀念論叢, 1965
- 전병훈, 정신철학 통편(精神哲學 通編), 1919