When people judge their lives as meaningful, what is this judgment about? Drawing on recent tripartite theoretical accounts of meaning in life (MIL), we tested the separate contributions of coherence (or comprehension), purpose, and existential mattering (or significance) as potential precursors of people's self-reported evaluations of MIL. In Study 1 (N = 314 social media users), we developed brief acquiescence-free measures of these constructs, confirming that sense of coherence, purpose, mattering, and MIL judgments were distinct from each other and from related constructs (sense of control, belonging, self-esteem, self-competence, mood). In Study 2 (N = 168 students) and Study 3 (N = 442 Prolific Academic respondents; preregistered), we collected longitudinal data to test temporal relationships between coherence, purpose, mattering, and MIL judgments over a 1-month time lag. In both studies, sense of mattering consistently emerged as a significant precursor of MIL judgments, whereas sense of purpose and coherence did not. We conclude that researchers and practitioners should pay more attention to the relatively neglected dimension of existential mattering, beyond their more common emphases on coherence or purpose as bases of meaningfulness. (PsycINFO Database Record (c) 2020 APA, all rights reserved).