In this chapter we learn about the classification of organic compounds, then we study about alkanes : nomenclature and isomerism, preparation, physical and chemical properties, conformations (Sawhorse and Newman projections). Then we study about alkenes : structure of double bond, nomenclature, isomerism, preparation, physical and chemical properties. Then we know about alkynes : structure of triple bond, preparation, physical and chemical properties. Then we study about aromatic hydrocarbon : nomenclature and isomerisation, structure of benzene, aromaticity, preparation of benzene, physical and chemical properties. Finally we know about carcinogenicity and toxicity.