The nasal cavity represents a suitable administration route both for local and systemic treatments. Conventional nasal formulations (liquid, solid, semisolid) show a limited residence time responsible for an incomplete drug absorption with consequent impaired therapeutic efficacy. In situ nasal gels represent a suitable formulative strategy able to overcome this problem. These formulations are liquid at room temperature, making an easy administration, and become gel once in the nasal cavity. This is possible thanks to the use of polymers able to form a viscous gel under specific stimuli as temperature, pH, ions in the nasal fluid. The chapter illustrates the evolution from conventional nasal formulations to innovative in situ gel delivery systems and the advantages of such formulations. It presents also recent approaches, based on the combination of in situ gels with nanocarriers, useful to protect the drug either improve the biopharmaceutical properties and promote a controlled release. The safety aspects have been examined as well.