In this talk I'll discuss our work on mitochondrial variability. Mitochondria serve as power stations for the cell and a conventional view has treated them as isolated organelles. In fact they are very dynamic: networking, fissioning, fusing, being consumed and being generated. We recently found a surprising experimental connection between a marked variability in the average rate of transcription of cells in a population and a marked variability in their mitochondrial content. I'll discuss our mathematical and computational attempts to summarize this data. They suggest the existence of a partly-heritable factor which is connected to cell-to-cell variability. I'll then move on to discussing how the genetic content of mitochondria might vary through time and make connections with disease.