TractoR con­sists of a set of R pack­ages, along with a script­ing sys­tem which provides ac­cess to the un­der­ly­ing code for non-useRs and those who wish to per­form only “stand­ard” tasks. This page de­scribes the gen­eral set-up of TractoR, and how it can be used as a gen­eral pur­pose lib­rary for work­ing with mag­netic res­on­ance im­ages. It also de­scribes how the in­ter­face between the shell and R works, and how you can write your own ex­per­i­ment scripts for use with the tractor shell pro­gram.