In the beginning it seemed to us that someone was missing and that something was amiss. He was often mentioned, occasionally discussed, but seldom cited or credited explicitly. And when he was acknowledged, it was sometimes for reasons that seemed anachronistic and misleading. His influence could be felt in a number of areas of our discipline, but few scholars seemed to know just how, just where, and to what extent. We discovered, almost accidentally, that we shared an interest in his legacy, in unravelling at least some portion of this riddle. Shortly thereafter, we began discussing ways in which, by pooling our resources with those of interested others, we could move closer to a res­ olution. Put simply, the protagonist of this riddle is Ludwig Wittgenstein (1889-1951), the son of a wealthy Viennese industrialist, the influential Cantabrigian philosopher, the rural Austrian schoolteacher. And the subject of our study is his largely unexplored legacy for developmental psychology. Although Wittgenstein's thought seemed to hold special promise for the study of human development, the philosopher and his work could walk virtually unrecognized through the landscape of contemporary developmental issues.