  We introduce a new general construction, denoted by $R\JoinE$, called the
amalgamated duplication of a ring $R$ along an $R$--module $E$, that we assume
to be an ideal in some overring of $R$. (Note that, when $E^2 =0$, $R\JoinE$
coincides with the Nagata's idealization $R\ltimes E$.)
  After discussing the main properties of the amalgamated duplication $R\JoinE$
in relation with pullback--type constructions, we restrict our investigation to
the study of $R\JoinE$ when $E$ is an ideal of $R$.
  Special attention is devoted to the ideal-theoretic properties of $R\JoinE$
and to the topological structure of its prime spectrum.
