Small molecule drugs continue to dominate our collective ability to treat disease. However, the pharmaceutical industry faces challenges on several fronts, and increasing productivity has been framed as the grand challenge for the sector. Against a background of increasingly cost-constrained healthcare systems, the cost of launching new drugs is increasingly high (recently estimated at £1.8 Bn for each new drug!). In order to improve productivity in drug discovery, it is necessary to develop innovative new medicines that address currently unmet medical needs. Protein-protein interactions represent a significant untapped, but challenging, opportunity for treating diseases including cancer, inflammatory disease, cardiovascular disease and infection. Drugs function by binding to a protein target within the body. Most existing small molecule drugs bind to well-defined pockets in proteins - analogous to a key fitting into a lock. In stark contrast, the design of drugs to inhibit protein-protein interactions generally requires a fundamentally different type of interaction of the drug with its protein target - analogous to a hand gripping a ball. Thus, the development of effective drugs that target protein-protein interactions raises new challenges that need to be met in future drug discovery. This programme will develop new tools and understanding that will facilitate future drug discovery against protein-protein interactions. We will develop computational tools to classify protein-protein interactions according to their underlying 3D structure and the probability that they can be inhibited using small molecules. We will then exploit these computational tools to design classes of small molecule that can be prepared readily using state-of-the-art synthetic methods, and that are predisposed to target different types of protein-protein interaction. The resulting small molecule inhibitors will be made available to biological researchers to help understand the role of protein-protein interactions in disease. In addition, the new tools will be made accessible to the research community to facilitate the early-stage discovery of small molecule drugs that target protein-protein interactions. The programme will benefit from the input of major pharmaceutical companies, smaller drug discovery companies, a not-for-profit drug discovery organisation, and international academics. The involvement of a wide range of experts is essential because of the increasing trend for early stage drug discovery to be conducted by a range of organisations (both industry and academic), especially for more challenging target classes. Thus, together with wider research community engagement, we will ensure that the required future capabilities for early-stage drug discovery against protein-protein interactions are met.