The main aim of this paper is to highlight the need to address the conceptual problem of “implicit knowledge” or “implicit cognition” —a notion especially important in the study of the nonverbal minds of animals and infants. We review some uses of the term ‘implicit’ in psychology and allied disciplines,and conclude that conceptual clarification of this notion is not only lacking, but largely avoided and reduced to a methodological problem. We propose that this elusive notion is central in the study (...) not only of animal and infant minds, but also the human adult mind. Some promising approaches in developmental and evolutionary psychology towards innovative conceptualisation of implicit knowledge remain conceptually underdeveloped and in need of reconsideration and re-elaboration. We conclude by suggesting that the challenge of implicit cognition and nonverbal minds will only be solved through a concerted interdisciplinary approach between psychology and other disciplines. (shrink)