Natural and synthetic cyclopropanes bearing simple functionalities are endowed with a large spectrum of biological properties ranging from enzyme inhibitions to insecticidal, antifungal, herbicidal, antimicrobial, antibiotic, antibacterial, antitumor and antiviral activities.The simple 2-substituted 1-aminocyclopropanecarboxylic acids (ACCs) are currently attracting special attention because of their potential use in conformationally restricted peptides, providing biosynthetic and mechanistic probes. As the immediate biosynthetic precursor of ethylene, the phytohormone that initiates and regulates many aspects of plant growth (germination, inhibition, senescence, fruit ripening, etc.), the parent ACC, structurally related to glycine, is a potent and selective ligand of the glycine modulation site coupled to the N-methyl-D-aspartate (NMDA) receptor, one of the four different receptors that mediate the action of the excitatory amino acids (EAA) in the brain transmitter systems; thus, such amino acids have also been proven to be useful in neurochemical studies. The mechanisms responsible for the diverse specific biological activities of compounds containing three-membered carbocyclic moieties are also being discussed.