The nature of roots and their role in linguistic theory has been the topic of extensive discussion for many years. A number of decompositional theories have proposed that roots are among the basic building blocks of word formation, yet they do not agree on their specific characteristics. The present paper approaches the issue from a different angle, namely through the lens of language contact. It will provide two case studies of language mixing word-internally and in compounds, drawing especially on mixing involving Greek, English, German, and Norwegian. The claim is that studying word formation processes where properties of more than one language are involved offers a unique window onto the basic word formation mechanisms and in particular onto the nature of roots.