Mitochondrial DNA plays a crucial role in cellular homeostasis; however, the 
molecular mechanisms underlying mitochondrial DNA inheritance and propagation 
are only beginning to be understood. To ensure the distribution and propagation 
of the mitochondrial genome, mitochondrial DNA is packaged into macromolecular 
assemblies called nucleoids, composed of one or more copies of mitochondrial DNA 
and associated proteins. We review current research on the mitochondrial 
nucleoid, including nucleoid-associated proteins, nucleoid dynamics within the 
cell, potential mechanisms to ensure proper distribution of nucleoids, and the 
impact of nucleoid organization on mitochondrial dysfunction. The nucleoid is 
the molecular organizing unit of mitochondrial genetics, and is the site of 
interactions that ultimately determine the bioenergetic state of the cell as a 
whole. Current and future research will provide essential insights into the 
molecular and cellular interactions that cause bioenergetic crisis, and yield 
clues for therapeutic rescue of mitochondrial dysfunction.