Infant-directed speech (IDS) is the particular voice register observed in the majority of parents in interaction with their infants and differs from natural speech used in conversations with adults by showing exaggerated prosodic features. These prosodic features are supposed to have effects on regulating infant arousal and attention, fostering infant pre-linguistic and linguistic competences and enhancing the expression of positive affect. The present set of meta-analyses was conducted to test these associations and the role of moderators during the first two years of infant life. The results confirmed an overall association between IDS prosody and infant outcomes with prosodic values typical of IDS associated with better outcomes. This association was confirmed for attentional, pre-linguistic and linguistic outcomes with a greater effect on pre-linguistic than linguistic outcomes. An insufficient number of studies was found to test the association with infant emotion expression. Many limitations in the existing body of literature were found, such as a lack of empirical papers exploring IDS prosody in relation to infant outcomes using natural observations. The results and limitations were discussed in light of the necessity to examine the interplay between the quality of IDS prosody and other aspects of parental communicative and care giving competences. To do so, the contribution of scholars from different fields is needed with the aim to fully understand the multidimensional determinants and influential mechanisms of IDS. (C) 2017 Elsevier Inc. All rights reserved.