This dissertation seeks to address the question of how contemporary performers and experts understand the medieval repertoire known to us as Gregorian chant. This medieval repertoire (also known as Franco-Roman) is understood here to be abstract musical and non-musical information in medieval manuscripts. It differs from classical western music repertoires by a lack of adequate original performance instructions. It becomes audible through performer’s realisation of his or her personal conceptualisation. This study observes both conceptualisation and practice of the repertoire through the answers of 127 respondents to an online sociological questionnaire and 35 solo recordings of the Gradual Haec dies. The study also involves a heuristic experiment to find connections between conceptualisation and practice. This research is multidisciplinary, combining sociology and musical acoustics. The sociological approach includes quantitative statistical and qualitative methods. Ideas of musical acoustics are applied to measure digitally the temporal structure of solo recordings of Gregorian chant. The analysis of the results of the questionnaire showed that there are certain patterns in evaluating what Gregorian chant is and what is important for a good performance of that repertoire. There was more similarity in understanding what the repertoire is than what the interpretational preferences are. Measuring the solo recordings showed that although there is a large variety in temporal understandings of the performed music, most performers tend to perceive performed music in one durational category. For those who have two basic durational categories it seems to be a result of agogical preferences rather than perception of two durational categories. The comparison of conceptualisation and practice showed that the strongest link between these two is in agogical variety. It was not possible to find similarly significant connections between conceptualisation and other features of practice – tempo values and the number of basic note values. This research project has demonstrated that a multidisciplinary approach to Gregorian chant can reveal new aspects in the study of the repertoire in terms of approach and understanding.