We know little about the relationships that matter to emerging adults. This preregistered report elaborates our plan to survey 200 emerging adults (approximately half male) to better understand the role of significant others. First, we plan to ask emerging adults to list individuals who matter and we will code the open-ended text for relationship type. Second, we will use an adapted version of Schneck’s (2009) Mattering Scale to assess mattering among five common close relationships (i.e., mother figure, father figure, partner, best friend, sibling). We predict that mattering of partner and best friend will be highest, mothers will matter more than fathers, and siblings will matter least. We hypothesize failing to mention a relationship in the open-ended portion will be related to lower mattering of that relationship. Finally, we anticipate better well being and less loneliness when the list of those who matter is longer and when significant others matter more.