Mitochondria typically exhibit an oblong form and range in size between 1 and 10 micrometers in length. The organelles exhibit significant flexibility, however, and when live cells are examined it quickly becomes clear that mitochondria are almost continuously shifting shape and moving throughout the cytosol. Mitochondrial movement appears to be associated with the cellular network of microtubules. The dynamic activity of mitochondria was visualized in the digital video sequences presented in this section with mCherry fused to a mitochondrial targeting signal. The cell nucleus was targeted with a mEmerald-H2B fusion.