This master thesis investigates the role of private autonomy and the phenomenon of contractualisation in the sphere of marital property, especially in relation to the tools for managing marital property and their suitability to the constitutional principles of the free development of the individual and the freedom to create a family model that meets one s own interests. The dynamism of contemporary marital relationships reinforces the availability and capacity of the spouses to build their existential project, their communion full of life, including with regard to property aspects and the marital property regime. In this context, the main object of study is whether there is a place, in the national legal system, for a legal figure such as the postnuptial agreement, a bilateral legal agreement between the spouses in which it would be possible to establish, even after the marriage has been celebrated, new rules on the acquisition, administration and sharing of assets in the future. Based on the civil-constitutional law s re-reading of the role of the family in the light of the 1988 Federal Constitution as an instrument for the free development of the personality of its members, we proceed to critically examine the treatment given by Brazilian law to the marital property regime and the system for changing it, highlighting the contrast between the freedom granted to the couple to build their unique property status at the beginning of married life and the restrictions on the exercise of this freedom during the course of the marriage. This paper then sets out to reflect on the postnuptial agreement as an alternative to the current regulation without any legislative changes being necessary. This analysis focused on the possibility of de-judicialization the procedure and on the usefulness and function of the postnuptial agreement as an tool for managing the assets of the marital partnership, examining its presuppositions of validity and efficacy, the remedies available in the legal system to protect pathological situations and its content, in order to demonstrate, based on bibliographical reading and the exploratory-deductive method, the utility and legality of postnuptial agreements in the light of civil constitutional methodology and to analyze the consequences of their use.