This chapter provides an introduction to the collection, analysis, and visualization of mouse-tracking data using free, open-source software. It shows how to create mouse-tracking experiments using the graphical experiment builder OpenSesame in combination with the mousetrap plugin. The chapter demonstrates how a mouse-tracking experiment can be created in OpenSesame. The mouse sensitivity settings cannot be adjusted directly within OpenSesame, but need to be set in the computer’s system preferences. The mousetrap R package represents mouse-tracking data in a specialized data structure, a mousetrap data object. This allows the package to store and process mouse trajectories efficiently, and to link them to other information collected during the study. In addition to curvature, mouse-tracking studies have also used the complexity of the movement as an indicator of response competition. In mouse-tracking studies, participants’ cursor movements are recorded as they choose between different options represented as buttons on a computer screen.