  Motile cilia are a striking example of functional cellular organelle,
conserved across all the eukaryotic species. Motile cilia allow swimming of
cells and small organisms and transport of liquids across epithelial tissues.
Whilst the molecular structure is now very well understood, the dynamics of
cilia is not well established either at the single cilium level nor at the
level of collective beating. Indeed, a full understanding of this requires
connecting together behaviour across various lengthscales, from the molecular
to the organelle, then at cellular level and up to the tissue scale. Aside from
the fundamental interest in this system, understanding beating is important to
elucidate aspects of embryonic development and a variety of health conditions
from fertility to genetic and infectious diseases of the airways.
