Nitrogen-containing compounds are used as structural components of pharmaceuticals and agrochemicals due to their high biological activities. There are many nitrogen-containing chemicals, from simple structured compounds as pyridine bases to complicated compounds as pharmaceutical ingredients and their number is growing rapidly year by year. Among the nitrogen containing compounds, pyridine bases are produced in by far the largest quantity and are used in various applications as herbicides, insecticides, vitamins like nicotinic acid and nicotinic acid amide, pharmaceuticals and adhesives. Pyrazines are used in flavors and fragrances and pharmaceutical intermediates. Among them, 2-methylpyrazine is used as a raw material of anti-tuberculosis drug, i.e. pyrazinamide. Pyrrole is used as a raw material of polypyrrole rather than in pharmaceutical applications. Polypyrrole has attracted much attention recently as an electroconductive polymer and its inexpensive production process is required. This article describes about such fundamental nitrogen-containing heterocyclic compounds as pyridine bases, pyrazines, piperidine, pyrrolydine, pyrrole, indole and imidazole.