This qualitative case study explored changes in one infant’s relationship development with her caregivers and peers in times of a major developmental transition, specifically from 10 months to 14 months. The data were collected through multiple sources, including observations, interviews, documents, and researcher journals, for a semester. Among the developmental achievements the infant gained in this study, her independent walking ability appeared to influence her relationships most. As her independent walking ability enabled the infant to gain a greater access to peers and caregivers, her presence in the room and social preferences for the people also appeared to change. The infant seemed to enjoy more playbased and group interactions with both peers and caregivers rather than emotion-based and dyadic interactions. The results of this study provided an insight into the multifaceted relationship development process, such as the connection between infant development and relationships and the association between infant-caregiver relationships and infant peer relationships.