The authors describe the development and initial psychometric properties of the Friendship Motivation Scale for Children, a new scale designed to assess four dimensions of self-determination (i.e., intrinsic motivation, identified regulation, external regulation, and amotivation) in preadolescents and early adolescents' desire for friendships. The results--obtained with a sample of 490 fifth-, sixth-, and seventh-grade boys and girls--confirmed the factor structure of the scale and revealed adequate internal consistency and test-retest stability. Indicators of construct validity included (a) correlations among the four subscales displaying a simplex pattern, and thus supporting the underlying theoretical model (i.e., self-determination continuum); (b) friends generally reporting similar levels of friendship motivation; and (c) children more self-determined in their friendship motivation reporting more prosocial and less hostile goals in friendship conflict situations and reporting fewer feelings of loneliness. Girls reported greater self-determined friendship motivation than boys, and girls with greater self-determination were preferred by their peers as play-work companions.