The development of relationships by private non-profit organizations (NPOs) with companies is fundamental to their sustainability. However, relational marketing and the definition of fundraising and communication strategies tend to be under-explored, resulting in punctual relationships with donors. This paper proposes to explore ways of developing relationships between NPOs and companies. After a systematization of the main contributions present in the literature, a qualitative and exploratory study was presented, in which semi-structured interviews were conducted with 8 NPO managers with different fields of activity and 16 managers of small, medium and large companies, all with headquarters in the district of Aveiro. The results show that what drives companies to support NPOs are essentially non-material benefits, such as the emotional impact on employees and other stakeholders. There are clear differences between small and large companies, the latter being more prone to formal relations. It was verified, however, that even the occasional supports can be recurrent and repeated, lacking the capacity to protocol the relation. Overall, the data offer interesting clues to NPO staff, namely resulting from a comparison of the different perspectives of the participants.