Abstract: Dynamic Nuclear Polarization (DNP) is a method of enhancing the NMR signal by microwave irradiation (MW) on unpaired electrons added to the sample as stable radicals. DNP experiments on samples with several types of nuclei can sometimes result in interesting phenomena such as polarization transfer between the nuclei or enhancement of one nucleus during MW irradiation at the DNP transitions of another nucleus. I will discuss the theory behind these phenomenon, and show experimental examples.