At the critical juncture between words and grammar lie verbs. Verbs appear in children’s earliest vocabularies (Choi, 1998; Choi & Bowerman, 1991; Choi & Gopnik, 1995; Fenson, Dale, Reznick, & Bates, 1994; Nelson, 1973; Tardif, 1996). They also serve as the architectural centerpiece of the sentence, specifying argument structure. How young children learn verbs is thus fundamental to our understanding of language acquisition. Most of the research on lexical acquisition has focused on nouns. The tides, however, are turning. Research from the past several years is beginning to illuminate the verb learning process. This chapter focuses on what children know about the conceptual foundations for verb learning. Though the field is still in its infancy, general (though not unanimous) consensus is emerging: learning verbs is hard. This fact is well documented in the literature and in many of the studies cited in this volume. By way of example, in laboratory tasks, infants appear to fast-map nouns at an earlier age than verbs (Golinkoff, Hirsh-Pasek, Bailey, & Wenger, 1992; Golinkoff, Jacquet, Hirsh-Pasek, & Nandakumar, 1996). Even in languages where verbs occur in the prominent, sentence final position, or in isolation as the result of argument drop, children tend to learn verbs later than nouns (eg, chapter 17, this volume; Au, Dapretto, & Song, 1994; Bornstein et al., 2004; Caselli, Bates, Casadio, & Fenson, 1995; but see Tardif, 1996). When choosing between a novel object and a novel action, children as old as 5 years have difficulty determining the correct referent for a novel verb in both English and Japanese (Imai, Haryu, & Okada, 2002, 2005; Meyer et al., 2003). Finally, even adults observing interactions between mothers and children on muted videos are less successful at picking out correct referents for verbs than for nouns (Gillette, Gleitman, Gleitman, & Lederer, 1999; Snedeker & Gleitman, 2004).