In conclusion, this chapter provides a review of paranasal sinus anatomy and discusses the physiology of mucociliary transport and abnormalities observed in patients with CRS. Normal mucociliary transport is essential for the maintenance of healthy sinuses. This is well illustrated by PCD in which a congenital abnormality in ciliary function leads to, among other manifestations, CRS and bronchiectasis. A decrease in mucociliary clearance has been demonstrated in most studies of CRS, with the bulk of evidence suggesting that the decrease is secondary rather than a primary event. Mucostasis, hypoxia, microbial products, and mediators and toxic proteins generated during chronic inflammation probably all contribute to diminished mucociliary function. These factors decrease mucociliary function by direct toxic effects on cilia, ciliary loss, other ultrastructural alterations in the epithelium and changes in the viscoelastic properties of mucus. Studies of patients before and after surgical restoration of sinus ventilation have shown that mucociliary function improves gradually over 1-6 months postoperatively. The slower than normal rate of recovery of mucociliary clearance after surgery highlights the importance of careful postoperative medical and surgical management which is discussed in Chapters 19 and 20.