Heterocycles are important constituents of natural compounds, synthetic medicines and are known to play a vital role in number of chemical and bio- chemical processes.They have extensively been studied in different areas of chemistry including the pharmaceutical and chemical industries. With respect to biological applications,these are found potent anti-inflammatory, analgesic, anti-pyretic, anti-microbial anti-viral, herbicidal, fungicidal, anticancer, anti-diabetic, anti-hypertensive and anti-oxidant agents. These derivatives have also been reported as synthetic intermediates for drugs, as stabilizers in rubber vulcanization and corrosion inhibitors.The book is divided in to IIIchapters. Introduction and Literature Review on the Synthesis of Thiazine Derivatives are described in chapter-I.The II chapter deals with Novel Synthesis and Antimicrobial Evaluation of 3-nitro -N-(4-oxo-2-phenyl-2H-1,3-Benzothiazin-3(4H)yl) Benzamide Derivatives while Chapter-III deals with Synthesis and Antimicrobial Activity (2E)-2-benzylidene-2H-1,4-Benzo- thiazin-3(4H)-one Derivatives which will be beneficial to Scientists who are working in Medicinal and pharmaceutical research.