There are numerous review articles on electron spin resonance spectroscopy (ESR), as well as on the application of this technique to biological systems. 1 10 For the research worker already involved in the area of paramagnetic resonance, these excellent reviews offer a great deal of insight into and discuss in depth the application of paramagnetic resonance spectroscopy. Yet, we are not aware of any work whose primary goal has been to introduce researchers to the practical considerations of paramagnetic resonance. Since we are both “chemists” who employ ESR to study biological problems and have had to go through some trying experiences as we learned about this technique and struggled to introduce our students to it, we feel we are in a position to save the newcomer some time by considering a more practical approach to paramagnetic resonance.