There were 7032 children in out-of-home care in 2018 in Portugal. Of these, only 2.8% were in foster care, despite this being the recommended response according to legal regulations. It is critical that more families be encouraged to become foster carers and also that experienced carers stay in the system to create a sustainable programme. How is the will to foster a child maintained? What can we learn from foster families’ experiences to improve childcare and the child protection system? The methodology of this study was based on interviews with foster carers. The analysis was inspired by grounded theory. We found three types of foster families, classified according to their will to leave or remain in foster care—unconditional, hesitant, or retired. The results suggest that the key elements for foster carers to remain in the foster care system are (i) their level of satisfaction with how the previous placement concluded, (ii) keeping in touch with the ex-foster child, (iii) the feeling of acknowledgement by all the stakeholders, and (iv) the quality of social services as well as the support of the professional teams.