In 1992, during the 15th Conference of the International Musicological Society, a round table about «Spanish and French Theater in Italian Opera of the Seventeenth Century» took place in Madrid. It was a seminal moment in the discussion about the influence of Spanish Siglo de Oro Theater on the Italian Opera of the Seventeenth Century. This influence is today beyond question and is being revealed as an important aspect to understand both the success of Venetian Opera and the dissemination of Siglo de Oro Theater outside Spain. This article aims at illustrating and discussing the results of twenty years of scholarly research on the subject; it also suggests new paths of investigation.