The integration of the residential function beyond the limits of the urban and developable land in the legislative frameworks has had a distinct and incomplete character. Faced with an identical phenomenon in general, called urban sprawl, the competent governments in this matter within the Iberian Peninsula have opted for a dissimilar assimilation of it, materialized in different legal and instrumental mechanisms. The objective of this paper is to present the different ways of understanding and regulating this new urban model by the Portuguese state government and the regional autonomous governments in Spain. To do this, a comparative analysis is carried out on the criteria for the classification of undeveloped land and a review of the most paradigmatic tools for the management of periurban and rurban development. The works indicate a position that is still indeterminate and, sometimes, contradictory. In spite of this, there is a tendency towards the regulated inclusion of the residential function outside the geographical contexts that have traditionally supported it. [ABSTRACT FROM AUTHOR]