By contrast with field-to-cable coupling, crosstalk is a near-induction mechanism by which two wires or PCB traces, belonging to different circuits and running in parallel can couple transversally, a certain % of the “culprit” wire voltage appearing on the ‘victim’ wire. Appropriate, simple equations, figures, and table of values are showing the physics of the “crosstalk.” This chapter concludes with three additional key rules to go along with the “field-to-equipment” radiation coupling.