The idea behind this project came to me when my organ teacher, Professor Hans-Ola Ericsson, introduced me to “Magnificat,” an organ piece by Swedish composer Torsten Nilsson (1920-1999). Nilsson's music spoke to me, and therefore I wanted more. In this thesis I study one of the pieces from the collection “Septem Improvisationes pro organo,” the piece for Good Friday, “Crucifigatur,” composed in 1968. In the introduction to this thesis, I ask if it is possible to identify a performance practice for this piece in particular, and if elements from this practice also can be applied to Nilsson's organ music in general. One of my objectives is to investigate how my own interpretation is influenced by the knowledge I acquire: How can I create a personal interpretation which is also rooted in the existing interpretative tradition for this piece? After a general description of the nineteen-sixties' musical context and a biography of Nilsson, I examine the different sources and the methods pertinent to my research. Besides analysis of the score, I have also analyzed several recordings of “Crucifigatur” and my lessons with distinguished Nilsson interpreters Hans-Ola Ericsson and Erik Boström. In the theory chapter I describe different approaches to the concepts of performance practice and musical interpretation, and explore the emergence of modern musical notation, since we find elements of this kind of notation in “Crucifigatur.” Finally, I make a comparison of my own recording against those of other interpreters. My recording of “Crucifigatur”, which makes up the main artistic results of the project, is analyzed in the light of these findings.