This book highlighted the methods used for the syntheses of thiosemicarbazide and their metal complexes. Molecular modelling for all prepared compounds was investigated. Dissociation and formation constants were calculated for ligands and complexes respectively. In vitro and in vivo studies for thiosemicarbazides showed high potent antitumor activity. Finally, this book reported thiosemcarbazide derivatives as organic chelates (which are not pollutant for water media and may have biological importance) for the separation of about 100% of Hg2+, Mn2+ and Cd2+ ions.