The AAA ATPase, p97 achieves its versatility through binding to a wide range of cofactor proteins that adapt it to different cellular functions. The heterodimer UN (comprising Ufd1 and Npl4) is an adaptor complex that recruits p97 for numerous tasks, many of which involve the ubiquitin pathway. Insights into the structural specificity of p97 for its UN adaptor are currently negligible. Here we present the solution structure of the Npl4 ‘ubiquitin-like’ domain (UBD), which adopts a ß-grasp fold with a 310 helical insert. Moreover we performed a chemical shift perturbation analysis of its binding surface with p97N domain. We assigned the backbone amides of p97 N domain and probed both its reciprocal binding surface with Npl4 UBD and its interaction with the p97-binding region of Ufd1. NMR data recorded on a 400 kDa full-length UN-hexamer p97 complex reveals an identical mode of interaction. We calculated a structural model for the p97 N–Npl4 UBD complex and a comparison with the p97-p47 adaptor complex reveals subtle differences in p97-adaptor recognition and specificity.