The design of selective fluorescent molecular sensors for cations is a subject of considerable interest because of their numerous potential applications in analytical chemistry, biology, medicine (clinical diagnosis), environmental chemistry, chemical oceanography etc. Most fluorescent molecular sensors consist of a cation recognition unit (ionophore) linked to a fluorophore; thus they are often called fluoroionophores. Also this book address graduate students of chemistry and analytical science about the structural and elucidation and synthesis and characterization of organic substances using sophisticated analytical instruments. This book also address the possibility of developing calixarene based fluoroionophore and their ion recognition property.