The overarching goal of the present study was to trace the development of mirror self-recognition (MSR), as an index of toddlers' sense of themselves and others as autonomous intentional agents, in different sociocultural environments. A total of 276 toddlers participated in the present study. Toddlers were either 16, 17, 18, 19, 20, or 21 months old at their first assessment and completed weekly MSR assessments over a period of 6 weeks (N = 1,577). The toddlers and their families were from one of four sociocultural contexts: A prototypical autonomous sociocultural context (urban German middle-class families, n = 82), two prototypical relational sociocultural contexts (rural Indian and rural Nso families living in subsistence-based ecologies, n = 54 and n = 80, respectively), or an autonomous-relational sociocultural context (urban Indian middle-class families, n = 60). In line with previous research, we hypothesized that the onset of MSR would be earlier in sociocultural contexts in which mothers value and support their toddlers' development of autonomy. In addition, we considered three factors that covary with culture and that might compromise the cross-cultural validity of MSR as a behavioral measure of toddlers' sense of themselves as independent agents: familiarity with mirrors, culture-specific norms of expressive behavior, and motivation for tactile exploration. Finally, we analyzed toddlers' reactions to their specular image (e.g., pointing, playmate, and experimenting behavior) across time and culture as well as their relation to MSR. The results indicate that MSR increased with age in all sociocultural contexts. In line with our hypotheses, MSR rates were higher in the autonomy-supporting cultural context (urban German, urban Indian) than they were in the relational cultural contexts (rural Indian, rural Nso). The sociocultural differences in MSR could not, however, be explained by differences in mirror familiarity or culture-specific norms of expressive behavior. The cross-cultural validity of MSR as an index of toddlers' sense of themselves as independent agents is further supported by positive associations between MSR and pronoun use in all sociocultural contexts. Cross-cultural variation in MSR could best be explained by caretakers' emphasis on autonomous socialization goals, followed by toddlers' motivation for tactile exploration. These findings enhance our current understanding of development in more general terms by adding one more puzzle piece to the emerging picture of culture-specific developmental pathways. In order to understand developmental processes, one must take into account caretakers' cultural models and exercise caution when generalizing beyond the specific sociocultural context at hand. (Contains 15 tables and 1 figure.)