The aim of this book is to analyse the legal and procedural unfeasibility of the institute of "desaposentação", i.e. renouncing a retirement pension in order to apply for a new, more advantageous benefit. To this end, it was necessary to examine the origin and concept of Social Security, as well as the types of retirement existing in the current Brazilian legal system. In addition, it was also necessary to analyse in detail the concept of disaposentation and then the main arguments that guide the discussion of the matter, including those used in the main judgement of the Federal Supreme Court - STF on the subject, promoting a systemic examination within the current social security and constitutional framework. Using comparative law, the solution given by Spanish legislation to the specific case was presented, identifying the possibility or not of its application in the Brazilian legal scenario.