In this thesis the usage of smell as a medium enhancing synesthetic perception is discussed. Common cross-sensory connections and their relevance for interaction design are examined. The research is based on discoveries made in psychology, cognitive science and philosophy. Smell usage in a cross-modal context is believed to enhance engagement and enrichen the interactive experience. In several experiments a correlation between the perception of color shape and smell could be detected. An approach to include synesthetic mappings in interaction design is introduced, analyzed and discussed. Finally, the cross-modal interactive art installation “The Color of Smell” is presented.