Christensen's book length poem Alfabet (1981), twice translated into Swedish, is the most famous Danish example of the so-called "systemic" poetry (systemdigtning), "arbitrary systems structure expressions themselves constructed like machines, understanding their own relativity in constructions which merely repeat themselves." (from History of European Literature by Annick Benoit-Dusausoy et al, 2000) The poem was formally structured around alphabets from "a" (apricot trees) to "n" (nights) and on the Fibonacci (c. 1170-c. 1250) sequence (0, 1, 1, 2, 3, 5, 8, 13, 21, 34...), in which every term is the sum of the two previous ones (0+1=1, 1+1=2, 1+2=3, 2+3=5...). Another famous example of combining systematic thought with poetry is Primo Levi's The Periodic Table (1975), which contrasted the Russian chemist Mendeleyev's periodical table of elements with autobiographical meditations. "The numerical rations exist in nature," Christensen once explained, "the way a leek wraps around itself from the inside, and the head of a sunflower, are both based on this series." The ninth alphabet is "i", and subsequently Christensen started the section with the word "ice" (in Danish "is") – "ice ages exist, ice ages exist, ice of polar seas, kingfishers' ice". The system ends with the letter "n", which has several meanings, including the case in which "n" is the symbol for the set of natural numbers.

Christensen contributed to such magazines as Krise og Utopi and Chancen, wrote children's book and a number of radio and television plays which have been produced in several countries. Christensen's poems have been set to music by the Danish composers Ib Nørholm and Svend Nielsen. She received numerous prizes, including the Nordic Prize of the Swedish Academy (1994), Der österreichische Staatspreis für Literature (1994), Grand Prix des Biennales Internationales de Poésie (1995), and Edvard Pedersens Biblioteksfonds Forfatterpris in 2003. In 1978 Christensen was appointed in the Danish Academy and in 1995 she become a member of Académie Européenne de Poésie. She was frequently mentioned as a candidate for the Nobel Prize in literature. Christensen died after a short illness in Copenhagen on January 2, 2009.

Author of books:

Lys: digte, 1962
Græs: digte, 1963
Evighedsmaskinen, 1964
Azorno, 1967 - Azorno (tr. by Denise Newman)
det, 1969 - it (tr. by Susanna Nied)
Intriganterne, 1972 (play)
Det malede værelse, 1976 - The Painted Room: A Tale of Mantua (tr. by Denise Newman)
Brev i april, 1979
Den historie der skal fortælles, 1979
Alfabet, 1981 - Alphabet (tr. by Susanna Nied)
Del af labyrinten, 1982 (essays)
Den store ukendte rejse, 1982
En vinteraften i Ufa og andre spil, 1987 (plays)
Digte, 1988
Lys og Græs, 1989
Mikkel og hele menageriet, 1990 (illustrated by Lillian Brøgger)
Sommerfugledalen, 1991 - Butterfly Valley: A Requiem (tr. by Susanna Nied)
Samlede digte, 1998
Hemmelighedstilstanden, 2000.