The intention of this tutorial is to introduce into the basic concepts of time‐of‐flight mass spectrometry, beginning with the most simple single‐stage ion source with linear field‐free drift region and continuing with two‐stage ion sources combined with field‐free drift regions and ion reflectors—the so‐called reflectrons. Basic formulas are presented and discussed with the focus on understanding the physical relations of geometric and electric parameters, initial distribution of ionic parameters, ion flight times, and ion flight time incertitude. This tutorial is aimed to help the applicant to identify sources of flight time broadening which limit good mass resolution and sources of ion losses which limit sensitivity; it is aimed to stimulate creativity for new experimental approaches by discussing a choice of instrumental options and to encourage those who toy with the idea to build an own time‐of‐flight mass spectrometer. Large parts of mathematics are shifted into a separate chapter in order not to overburden the text with too many mathematical deviations. Rather, thumb‐rule formulas are supplied for first estimations of geometry and potentials when designing a home‐built instrument, planning experiments, or searching for sources of flight time broadening. © 2016 Wiley Periodicals, Inc. Mass Spec Rev 36:86–109, 2017.