This book highlighted the methods used for the syntheses of thiadiazole compounds. The activity of thiadiazole and their synthetic importance were investigated. It also reported a theoretically study for the expected tautomeric behavior of 2-amino(imino)-1,3,4-thiadiazole to determine if it is acting either as amine or as semicyclic amidine. In this context, we reported herein the behavior of 2-aminothiadiazole towards some active reagents as a facile and convenient route to some fused or binary heterocyclic compounds containing a thiadiazole moiety. The methods of synthesis and the synthetic mechanisms of the aforementioned reactions were well presented and the structures of these compounds were assessed by analytical and spectral data. ABTS Antioxidant assay, Bleomycin-dependent DNA damage and antitumor activity methods were used for the evaluation of the biological activity of the investigated compounds.