N?ron models were invented by A. N?ron in the early 1960s in order to study the integral structure of abelian varieties over number fields. Since then, arithmeticians and algebraic geometers have applied the theory of N?ron models with great success. Quite recently, new developments in arithmetic algebraic geometry have prompted a desire to understand more about N?ron models, and even to go back to the basics of their construction. The authors have...