Ubiquitous in nature, cilia and flagella comprise near identical structures with similar functions. The most obvious example of the latter is motility; driving movement of the organism or particle flow across the epithelial surface in fixed structures. In vertebrates, such motile cilia are evident in the respiratory epithelia, ependyma and oviducts. For over a century, non-motile cilia have been observed on the surface of most vertebrate cells but until recently their function has eluded us. Gathering evidence now points to critical roles for the mono-cilium in sensing the extracellular environment and perturbation gives rise to predictable panoply of clinical problems. I will review the evidence for cilia function during development and examine the consequences of cilia dysfunction in disease (ciliopathies).