This chapter defines the technique to collect and analyze reaction time data using the MATLAB® software. Reaction time measures to probe the mind have been the backbone of experimental psychology at least since the time of Donders (1868). The basic premise underlying the use of reaction times in cognitive psychology is the assumption that cognitive operations take a certain and measurable amount of time. In addition, it is assumed that additional mental processes add linearly. If this is the case, increased reaction times reflect additional mental processes. It is assumed that for the time being this is a reasonable framework. Then, it is highly useful to have a program that allows to quickly collect reaction time data. The chapter reveals that there are different ways to measure time in MATLAB. One of the most convenient comes in the form of the functions tic and toc. They work in conjunction and effectively implement a stopwatch.