This thesis is a violinists study of diminutions (ornaments; improvisation around an already composed melody) composed by Johann Helmich Roman over the first movement of Archangelo Corelli’s violin sonata no 4 op 5. In order to perform the diminutions the author of this thesis made a transcription of Roman’s handwritten sheet music. This thesis also contains necessary background information for the subject, such as biographies over Roman and Corelli. In the end of the thesis the author is discussing why Roman wrote these diminutions, the author’s thoughts on performing them and if the transcription helped preparing the performance.