Cyclodextrins (CD) are currently employed in analytical and preparative separations of enantiomers of chiral compounds as well as in some areas of organic and biological chemistry, biochemistry and medicine. In addition, these compounds found broad use in pharmaceutical and food industries. So far, general understanding of mechanisms of formation of inclusion complexes of CD with various guests has been rather limited. This lack of knowledge seems to be associated with structural flexibility of CD and guest molecules. This paper reviews interactions involved in the formation of the host-guest complexes and summarizes roles of these interactions in the arrangement and stability of the complexes. It discusses roles of functional groups of the guest molecules in the complex formation and pays attention to enantioselectivity of the process. Some thermodynamic aspects of the complexation reactions of CD are included and briefly discussed.