We present a novel approach to the analysis of jazz solos based on the categorisation and annotation of musical units on a middle level between single notes and larger form parts. A guideline during development was the hypothesis that these midlevel units (MLU) correspond to the improvising musicians’ playing ideas and action plans. A system of categories was devised, comprising nine main categories (line, lick, theme, quote, melody, rhythm, expressive, fragment, void), 19 subcategories, and 41 sub-subcategories as well as syntactical rules to encode motivic relationships between units. A set of 140 monophonic jazz solos from various jazz styles (traditional, swing, bebop, hardbop, cool jazz, postbop, free jazz) was annotated manually, resulting in 4939 units in total. The median number of midlevel units is 32 per solo and 13.75 per chorus. The average duration is 2.25 s (SD = 1.57 s), in good agreement with the duration of the subjective present. Overall, the most common main category is lick (45.7% of all units), followed by line (31.5%), but distributions of the main MLU types differ significantly between styles and performers. About one quarter (M = 25.1%, SD = 15.3%) of the annotated units have motivic relations to preceding units. The mean length of consecutive motivic chains is 2.8 (SD = 1.4). The amount of motivic relations varies considerably between performers, but not between styles. Based on these first results, we discuss implications for jazz research and options for further applications of the proposed method.