This document summarizes the principles and applications of Mossbauer spectroscopy, also known as nuclear gamma resonance spectroscopy. It discusses how Mossbauer spectroscopy probes nuclei using gamma rays and measures gamma absorption spectra. It explains how nuclei in solid crystals can undergo nuclear resonance because they are bound and not free to recoil. The document also outlines several key parameters that must be satisfied for Mossbauer spectroscopy to be effective, including the energy of nuclear transitions and lifetimes of excited states. Finally, it provides examples of how Mossbauer spectroscopy has been used to identify iron oxide nanoparticles in magnetotactic bacteria.