Nurturing relationships with major donors is a priority for nonprofits, and “relationship fundraising” is the dominant paradigm. This grounded theory study addressed practical needs and a dearth of research by analyzing how fundraisers develop relationships. In a first-of-its-kind study, we interviewed 20 pairs of higher education fundraisers and major donors (n = 40) from multiple U.S. institutions. We discovered five tiers of relationships from a basic connection, personalized association, confident relationship, purposeful partnership, to a consequential bond. Fundraisers initiated the progression until the final tier; the theoretical model shows their intentionality in the relationships’ development. Major gifts occurred in all tiers. The model illustrates how fundraisers build relationships, explores donors’ expectations, and affirms the relational nature of major gift fundraising. It provides some of the only empirical evidence regarding major donors, and the relationship fundraising philosophy touted in practitioner literature. The analysis reveals connections to theories from social psychology and relationship marketing.