Here we examine the hypothesis that symbolic understanding across domains is mediated by a fundamental ‘symbolizing’ ability in young children. We tested 30 children aged 2-4 years on symbolic tasks assessing iconic and non-iconic word-referent and picture-referent understanding and administered standardised tests of symbolic play and receptive language. Children showed understanding of the symbol-referent relation earlier for pictures than written words, and performance within domains was correlated and, importantly, predicted by a marker of general symbolic ability (e.g. pretend play). Performance on picture and written word tasks was also unrelated to language comprehension. Thus, symbolic abilities in specific domains are underpinned by a general symbolizing ability which arises early in development.