Cilia and flagella are complex, but highly conserved, structures found on most cells of the human body. Mutations in proteins localized to cilia can cause a collection of human diseases including renal failure and retinal degeneration. Dr. Marshall begins with an overview of the complex internal structure of cilia and flagella and the machinery, called intraflagellar transport (IFT), required to build and maintain these structures. Mutations in motile cilia were known to cause several human diseases but it wasn’t until scientists began studying IFT in the green algae Chlamydomonas, that the key role of non-motile cilia in human health and development was recognized. Marshall describes how mutations in cilia and basal bodies can cause human diseases as different as renal failure and retinal degeneration.