Nasal drug administration is attractive noninvasive approach to rapidly achieve local or systemic effects of small molecular drugs, proteins, and peptides, as well as for nasal immunization and nose-to-brain targeted delivery. However, conventional nasal dosage forms such as nasal drops, sprays, and nasal powders, are often suboptimal to provide bioavailability higher than 10% of drug molecules with high lipophilicity, hydrophilicity, or molecular mass, due to the nasal mucociliary clearance mechanism. The most extensively investigated formulation strategy for improving nasal bioavailability is the development of mucoadhesive drug delivery systems. Novel nasal liquid preparations with in situ gelling polymers have been proposed as a promising concept suitable for convinient instillation, precise dosing, good spreadability, enhanced nasal retention, and achievement of controlled drug release. Furthermore, mucoadhesive polymeric nanoparticles (up to 300 nm) have been evaluated as carriers for increased nose-to-brain bioavailability. This chapter reviews widely used mucoadhesive polymers and their derivatives considered so far as components of nasal drug delivery systems, including: natural polymers (chitosan, cellulose, starch, xanthan gum, gellan gum, pectins, alginates, gelatin) and their derivatives, synthetic polymers (polyacrylates, polycarbophils), copolymers and polymer blends (physical mixtures, polyelectrolyte complexes, cross-linked polymers). Many of novel polymers enable enhanced permeation enhancement capacity, in situ gelling and drug delivery control in response to nasal temperature, pH, ions, or enzymes, thus providing significant improvements in bioavailability of both small molecules and macromolecules. The versatility of the concept grows continuously by combining such responsive (smart) polymers or by functionalization of polymers by targeting ligands. Future prospects in development of mucoadhesive polymers as pharmaceutical excipients for nasal application are also briefly overviewed.KeywordsNasalMucoadhesivePolymersSpreadabilityNatural