Another path to electron spin resonance spectroscopy (ESR) on single atoms and molecules is pursued within the ERC Consolidator Grant by Dr. Christian Ast. Here, ESR is combined with low-temperature scanning tunneling microscopy to investigate individual atomic and molecular spin systems. The spin degeneracy is lifted by an external magnetic field and then excited by a microwave. The measurement of the excited spin state is realized through a spin-polarized tip. The goal is to employ pulsed ESR to better understand the spin dynamics of interacting spin systems.