Insomnia is one of the most common sleep disorders affecting about 30% of adult population, while its prevalence is even higher among elderly and psychiatric patients. Pharmacological properties makes zaleplon the drug of choice for the short term treatment of insomnia, but its low aqueous solubility and intensive metabolism in liver are reducing its oral bioavailability to only 30%. Therefore, the aim of this work was to improve aqueous solubility of zaleplon through inclusion complexation and to develop a novel drug delivery system able to enhance its therapeutical efficiency. Spectrofluorimetric and phase solubility studies showed that parent β-cyclodextrin forms stable inclusion complexes with zaleplon, but aqueous solubility of the complexes formed was limited. Among chemically modified β- cyclodextrin derivatives, randomly methylated derivative was the most efficient, while the solubility and stability of zaleplon complexes with sulphobutyl- and hydroxypropyl-β-cyclodextrin was less pronounced. The inclusion complex formation in all cases was confirmed by 1H-NMR spectroscopy. The structure of the complexes formed was characterised by the presence of two different binding modes which existed simultaneously in the solution. The first and the dominant one occurs through inclusion of phenyl moiety of the drug into central cavity of cyclodextrin molecule, while the other involves the inclusion of the pyrazolo[1,5-a]pyrimidine ring of the drug. The formation of higher order complexes was not demonstrated. Thermodynamic studies showed that complexation of zaleplon with β- cyclodextrin and its randomly methylated and hydroxypropylated derivatives was enthalpy driven, while entropy driven complexation was observed in case of sulphobutyl-β-cyclodextrin. In all cases, inclusion complex formation was a spontaneous process. Addition of hypromellose enhanced significantly the solubilising and complexing potential of randomly methylated β-cyclodextrin due to ternary complex formation, while hydrophilic polymers had no effect on solubility and stability of zaleplon complexes with parent β-cyclodextrin. Binary and ternary zaleplon complexes with cyclodextrins and polymers tested were prepared by spray-drying. Differential scanning calorimetry, X-ray powder diffractometry and scanning electron microscopy showed only partial drug amorphization of the drug in binary and ternary complexes with β-cyclodextrin, while all complexes with randomly methylated β-cyclodextrin were completely amorphous. The inclusion complex formation in spray-dried products was confirmed by the solid state NMR. Binary and ternary complexes with randomly methylated β-cyclodextrin and hypromellose were the most efficient in increasing the dissolution rate of zaleplon. The use of mannitol as a soluble filler and ternary inclusion complex with randomly methylated β-cyclodextrin and hypromellose allowed formulation of tablets which released the complete drug dose in 5 minutes, providing fast onset of drug action. Highly soluble zaleplon complexes with soluble, polymeric β-cyclodextrin derivative were also prepared by co-grinding in high energy vibrational micromill. Co-grinding at frequency of 24 Hz resulted in an amorphous product which is readily soluble in water, forming inclusion complexes as demonstrated by 1H-NMR spectroscopy. Spray-drying technique was used to prepare pH-responsive zaleplon microspheres with delayed release properties as a novel drug delivery system for treatment of specific type of insomnia characterised with premature awaking and inability to fall asleep again. Matrix containing 80% of Eudragit S100 and 20% of glycerol monostearate was demonstrated to be optimal, preventing the drug release at high pH-values. The incorporation of 50% of the drug dose in form of binary inclusion complex with randomly methylated β-cyclodextrin ensured complete drug release in simulated intestinal media, with the zero-order release rate (k0=155 μg/min).