This chapter contains sections titled: Introduction Bonding in Cyclopropanes Molecular Geometry of Cyclopropane Derivatives Conformation in Substituted Cyclopropanes Ionization Potentials and Spectral Properties of Cyclopropane Derivatives Molar Refractivities and Dipole Moments Other Physical Properties The Cyclopropyl Group as a Substituent Transmission of Resonance Effects by the Cyclopropane Ring Addition Reactions of Cyclopropane Reactions of the CH Bond in Cyclopropane Recent Developments References