Relational reasoning broadly refers to how we assign symbolic meaning to stimuli based on their relationship to other stimuli. For example, the term and concept “tall” can only carry meaning relative to “short”. Charles Spearman referred to g as a generic factor of “cognition of relations” (1927, p.165) suggesting that relational reasoning may be central to general cognitive ability. The present article has two main aims. The first aim is to highlight that key researchers across several research traditions have independently converged upon the idea that symbolic cognition involves the ability to relate stimuli for purposes of adaptation, based on both their physical and symbolic properties. There is a large volume of research on relational reasoning of one form or another across several fields, often adopting a diverse range of terminology. For this reason, it is beyond the scope of the current paper to present an exhaustive systematic review of research on relational reasoning. Instead, we focus on key exemplars from each field to highlight a common focus on relational cognition as an opportunity for dialogue across fields when discussing and researching cognitive ability. Secondly, this article then aims to describe a behavioral account of relational reasoning called Relational Frame Theory (RFT) that may prove especially useful for training relational reasoning such that it can be applied across contexts. As such, it might provide a particularly promising avenue of research on far transfer cognitive training effects. Therefore, the overall thesis of this paper is that multiple fields have independently converged upon a relational reasoning account of cognition, but, also that RFT uniquely lends itself to promising training interventions to enhance relational reasoning ability.