Part-span factors are used as part of the prediction method in various Data Items relating to high lift-devices and control surfaces. ESDU TM 172 presents analysis and background information regarding the derivation of Figure 3 in ESDU 93019@ Figure 1 in ESDU 74012 and Figures 4 and 5 in ESDU 14004@ all of which give part-span factors. These figures have subsequently been used in a number of other Data Items. Firstly@ this Technical Memorandum presents analysis which provides a general derivation of part-span factors for both lift and rolling moment. Information is presented regarding the derivation of Figure 3 in ESDU 93019. Next@ background information is provided which gives the derivation of Figure 1 in ESDU 74012. An analysis is then presented which leads to the derivation of part-span factors for both lift and rolling moment for spoilers. Background to the derivation of Figures 4 and 5 in ESDU 14004 is presented. Finally a general overview is given which outlines the dependence of part-span factor on the type of high-lift device or control surface being used.