The MDM2 and MDM4 oncoproteins are both involved in regulating the tumour suppressor, p53. While the MDM2–p53 interface is structurally and biophysically well characterised, the MDM4-p53 interaction has only recently attracted researchers’ attentions. The goal of this project was to establish structural and chemical ground rules for the disruption of the interactions between the N-terminal domains of MDM2/4 and p53, which is an attractive anticancer strategy. In the current work, successful recombinant production and purification protocols for both the N-terminal domains of MDM2 (i.e. MDM2-N, residues 11-118) and MDM4 (MDM4-N, residues 14-111) have been established, yielding protein in sufficient quantity and quality for analysis using nuclear magnetic resonance spectroscopy (NMR). Two screening strategies were employed to identify small-molecule antagonists of the MDM2-N:p53 interaction. First, a virtual screening exercise identified several compounds that were shown (by NMR) to bind to MDM2-N with μM KDs. Docking studies supported by NMR chemical shift perturbation analysis suggested proposals for binding modes. The results are discussed in relation to the previously reported binding to MDM2-N of well-characterised inhibitors of the MDM2:p53 interaction such as Nutlin-3. Second, a fragment-based library was screened against MDM2-N using TROSY-type NMR spectra to monitor binding. Several hits were identified and the results are discussed with regard to the “druggability” of the MDM2-N p53 interaction. To better understand the p53-binding groove of MDM4-N, multidimensional NMR was used to investigate the structure and backbone dynamics of double-isotopically labelled samples of MDM4-N, both free (i.e. apo-MDM4-N) and in complexes with a p53-derived peptide or Nutlin-3. The apo-MDM4-N is more conformationally dynamic than MDM2, since it contains unstructured regions. These regions appear to become structured upon binding of a ligand. MDM4 appears to bind its ligand through conformational selection and/or an induced fit mechanism involving reorganization of key sub-sites within the binding groove. This study highlighted Abstract differences between Nutlin-3 and peptide binding that suggest the rational design of specific inhibitors of the MDM4:p53 interaction.