Abstract
This chapter provides a general overview and methodology of heteroaromatic tautomerism. This chapter discusses tautomerism, which can be divided in two main groups. In this chapter, two situations are found, depending on whether the result is consistent or not with the generally accepted situation regarding the tautomerism of already studied heterocycles of similar structure. The chapter is based on either general physical-organic chemical considerations or on theoretical calculations. The chapter highlights four major changes: (1)the standard application of high-level theoretical methods, (2) the massive use of X-ray crystallography, (3) the introduction of solid-state cross polarization and magic angle spinning (CPMAS) nuclear magnetic resonance (NMR), and (4) the increasing significance of proton transfer in the excited state.