The purpose of this study was to build upon the growing body of knowledge relating to music improvisation by investigating the processes used by high school music instrumentalists when improvising music and the factors that influence those processes. Many factors contribute to music improvisation skill and they must all be taken into account when investigating the music improvisation processes of high school music students. The theoretical framework of this study was based on the complex interactions that take place simultaneously between three identified ensembles of factors. The three ensembles of factors were: I . The student profile which included general information and detailed aspects of prior music experience. 2. Enabling skills which included audiation ability, the ability to play music by ear and kinaesthetic abilities. 3. Improvisation processes including, creative processes, cognitive strategies and group or solo contexts for music improvisation. Taking into account the exploratory nature of this study, the single embedded case study design, involving 12 high school music instrumentalists aged between 13 and 15 years, offered the necessary potential to cope with the wide variety of evidence. The formal survey was used to gather information that would establish a detailed profile of each student. The Test of Ability to Audiate and Ability to Play by Ear (TAAAPE) was used to measure students' ability to audiate and play music by ear. Similarly, in order to explore the relationships between improvisation processes, enabling skills and the profile of each student, the Improvisation Ability Test (IAT) was used. This test provided authentic music improvisation experiences in both group and solo contexts. Both tests were scored by two independent judges and the researcher. Finally, the focused interview was used to establish the cognitive strategies used by the students when undertaking the various music improvisation tasks. The ability of the case study design to handle both qualitative and quantitative data proved to be useful in this study. Two major findings emerged from the analysis of the data: 1. The first was that the processes used by this small group of students when engaged in music improvisation were unpredictable. 2. The second major finding relates to evidence that supports the theory of an interaction between the three ensembles of factors as presented in the theoretical framework of this study. However, contrary to what might have been expected, the study further indicated that the interaction of these factors, in the context of the music improvisation processes used by these individual students, did not follow or produce any specific patterns. It was not within the scope of this study to seek the emergence of a model for teaching music improvisation to high school music instrumentalists. However, it has opened the path for further research which could result in the development of such a model.