Surfactants play an essential role in our daily lives. Their form of usage varies from detergents and cleaning agents through disinfectants and solubilisers up to industrial applications such as paints, oil recovery, anti-corrosion protective coatings, etc. A special distinct class of surfactants is represented by a double-chain, double-head form of surfactant molecules, which are called gemini surfactants. Gemini surfactants show physicochemical and aggregation properties which are superior to those of conventional, single-chain surfactants. From the perspective of applications, an important group of gemini surfactants is represented by cationic gemini surfactants. They have found numerous applications in the various fields such as solubilisation, textile coating, organic and polymer synthesis, electrochemistry, paper industry, etc. One of the most developing areas of cationic gemini surfactants application is the field of pharmaceutical applications. Interaction of cationic surfactants with the oppositely charged cell membrane has been known for a long time. Cationic gemini surfactants turned out to be very efficient bactericidal and antimicrobial agents. Moreover, recent development in this field indicates a cancerostatic effect of cationic geminis through a selective interaction of cationic gemini molecules with cancer cells. Another revolutionary field of cationic gemini surfactants application is their interaction with an oppositely charged electrolyte such as DNA. The interaction of DNA with various positively charged systems such as cationic surfactants, polymers and lipids is of great importance with respect to gene transmission through a biological cell membrane to achieve a therapeutic effect in a cell nucleus. The ambition of this monograph is to provide a complex view of synthesis, structure-aggregation, properties-biological activity relationship and recent applications of cationic gemini surfactants in the pharmaceutical field. Individual chapters in the monograph discuss the synthetic preparation of cationic surfactants, the effect of the structure of these compounds on their physical and physicochemical properties, particularly their aggregation properties and associated phenomena. A significant part of this publication is devoted to gemini surfactants, a relatively new class of surfactants whose special and surprising properties increasingly continue to draw the attention of the research community. The final part of the monograph is oriented on the use of cationic surfactants in biomedicine and pharmaceutical applications, where a special emphasis is put on their antimicrobial and antineoplastic activities. Finally, cationic surfactants as potent non-viral gene delivery vehicles are analysed and evaluated. The monograph is intended to serve as a guide for scientists and students in the field of pharmaceutical research and chemistry of colloids and surfactants.