The monarchies of the Iberian Peninsula—Spain and Portugal—formed large multicontinental empires in the 16th century, which lasted until the beginning of the 19th, when independence movements divided them into various nations in the Americas. The functioning of these political constructs depended to a great extent on the capacity to create channels of communication that allowed information to be frequently and reliably transmitted and received. In turn, the progressive development of information policies was linked to the strengthening of the powers of monarchs and those close to them, which implies that one of the elements affirming the state during the modern era was its capacity to administer communication among its various agents. This was made concrete through the development of diplomacy and intelligence systems, including espionage. More than marginal and isolated actions, the use of spies and infiltrated informers in rival states was a recurrent instrument throughout the period and counted on the knowledge and agreement of the Iberian kings and their ministers. Although it is a research field that is still little visited, there has been a growth in research on the modern period, showing that societies were thirsty for information and looked for it to calculate ways of defending and strengthening the Portuguese and Spanish kingdoms.