This book compiles the theoritical studies done on cyclic peptidic and peptidomimetic compounds.Ab initio 'Hartree Fock Molecuclar Orbital' calculations have been done on cyclic compounds to determine their potential to play role as ion and drug carriers.Role of substituents and backbone type have been thoroughly studied to understand properties which facilitate ion selectivity and potential to cross Blood Brain Barrier.Lead compound has been suggested to selectively remove zinc ions from brain so as to reduce plaque formation responsible for Alzheimer's disease.Also, a suitable carrier has been suggested for extensively used drug,Levodopa used for treatment of patients suffering from Parkinson's disease. The work with cyclic compounds is extended to find out possibilities of self aggregation. Properties of cyclic compounds to self aggregate/assemble lead to formation of hollow tubular structures in nanorange.They also showed probability of carrying drugs inside them in an efficient manner without forming covalent bonds. This study reveals that cyclic compounds are very interesting systems with wide variety of applications and can be modified intelligently according to one's needs.