This is a translation of "Mémoir sur les Intégrales Définies, prises entre des Limites Imaginaires." by Augustin Louis Cauchy, available from www.e-rara.ch. You will need to be well versed in Integral Calculus and the theory of complex variables to be able to understand this memoir. It will also help if you are already familiar with the Residue Theorem. This memoir contains a plentiful number of applications of the Residue Theorem to real definite integrals.