This article focuses on the cross-linguistic lexical influence between English and Spanish. It begins by redefining the concept of cross-linguistic lexical influence as the impact that two or more languages have on each other’s vocabulary. It then presents a brief chronological survey of Hispanicisms in English and Anglicisms in Spanish, taking the Oxford English Dictionary (OED) and the Diccionario de la lengua española (DRAE) as the main sources, and examines some of the factors that affect the patterns of word interchange between these two languages. It argues that the historical and social milieu, mass media, information technology, prevailing attitudes to foreignisms, and the stance taken by dictionaries and official linguistic policy condition which words are borrowed, affect the phonological, orthographic and semantic forms of these borrowings, and impact the degree of their integration in the receiving language. The present study is the first to offer a cross-linguistic (bilateral) perspective on lexical borrowing, a novel approach that is of particular interest given the contrasting philosophical differences governing language policy and lexicographic traditions in English and Spanish. It demonstrates the importance of adopting a comparative approach in the study of lexical influence between languages.