This article seeks to reinvigorate research on firm age by providing the first comprehensive review of the construct. We provide evidence that certain long-held assumptions about age have changed as organizations have become increasingly temporary and discuss what this means for organizational research going forward. We inductively structured our review along five themes: [1] research on age-dependence in organizational mortality rates; [2] research on age-related differences in firm processes or structures; [3] research enriching the theoretical understanding of firm age; [4] research that includes firm age as a control variable; and [5] methodological issues in the study of firm age. Across these five themes, we identify important work, integrate what we know, identify gaps and inconsistencies, and offer recommendations for future research. We derive more specific recommendations for two streams of research in particular, namely, research on entrepreneurial success and failure, which is directly tied to the liability of newness, and the literature on temporary organizations, which is concerned with the intended and actual durations of firms.