In Freundschaft is a composition by , number 46 in his catalogue of works, which is playable on a wide variety of solo instruments.
A first version of In Freundschaft was composed on Sunday, 24 July 1977 in Aix-en-Provence as a birthday gift for Suzanne Stephens. This version was written for the clarinet, but Stockhausen immediately made a fair-copy transposition for flute, and it was this version that was first performed, one time each by two American flautists, Lucille Goeres and Marjorie Shansky, for Stephens’s birthday party in Aix on 28 July 1977. The first public performance, also of the flute version, was given by Lucille Goeres on 6 August 1977, in a concert by course participants of the Centre Sirius at the Aix Conservatory. Stockhausen reworked the composition on 27 April 1978, at which time he also made versions for oboe, trumpet, violin, and viola (). The premiere of the version for clarinet was given by Suzanne Stephens on 30 November 1978 as part of a concert Hommage à Olivier Messiaen, in the Salle Wagram, Paris, and the version for oboe was premiered by Heinz Holliger on 6 July 1979 in a Musik des 20. Jahrhunderts concert in the large hall of Funkhaus Halberg at the Saarländische Rundfunk in Saarbrücken. At around this time, Stockhausen adapted the clarinet version for the basset horn, with extended range to low C, and this version was first performed by Suzanne Stephens at a private gathering at the composer’s house on the occasion of his fifty-first birthday on 22 August 1979. Both the clarinet and basset-horn versions are authorised for performance on bass clarinet, and the first public performance of the extended-range version was given by the Dutch bass clarinetist Harry Sparnaay on 10 January 1981 in Haarlem (, 136–37).
In the following years, Stockhausen adapted the work for most of the other orchestral instruments. Between 7 and 10 January 1981, in collaboration with Warren Stewart, Stockhausen made a version for cello, which Stewart premiered at the Eastman School of Music on 23 April 1981. Even before this premiere, Stockhausen had adapted it, from 16 to 19 April 1981, as a new version for violin. A version for bassoon followed the next year, composed on 19 and 20 April 1982 for Kim Walker. During rehearsals, Stockhausen came to imagine the piece being played by a teddy bear, like the one he had had as a small child, only much larger. Walker had a costume made, and gave the premiere in the Wigmore Hall in London on 10 May 1982 under the title "In Freundschaft, for a teddy bear with bassoon". A version for trombone was requested by Mark Tezak, who finalized the details with Stockhausen during rehearsals in August and September 1982. Around the same time, John Sampen requested and performed a version for soprano saxophone, though Stockhausen made further adjustments the next year with the saxophonist Hugo Read. At the request of the hornist Alejandro Govea Zappino, a version for his instrument was prepared during rehearsals on 17 November 1983, but further changes were carried out up to 11 September 1984 and the premiere was only finally given by Jens McManama, hornist with the Ensemble InterContemporain, at a concert in Baden-Baden celebrating Pierre Boulez’s 60th birthday on 31 March 1985 (, 137). Even a version for alto recorder came into existence, at the instigation of Geesche Geddert, first in an exchange of letters, then in rehearsal with Stockhausen on 6 April 1984 (Geddert 1985, 416; , 137). The published score of the cello version can also be played on double bass, and a version for tuba also exists (, 25). In response to a suggestion by his trumpet-player son, Markus (who had put off attempting the work for 20 years), he replaced the original trumpet version with a new one for trumpet in E♭ with a special fourth valve. Markus gave the world premiere of this new version in Kürten on 31 August 1997 (, 8, 14, 20).