Professor Peter Donnelly tells us how genetics helps us to understand common diseases and develop new drugs. Understanding which variations in our DNA affect susceptibility to diseases can provide new insights into the disease process and lead to new treatments. Professor Peter Donnelly leads large collaborative human genetic studies, and his group develops and applies statistical methods to extract maximal information from the large datasets generated by genomic studies. Creative Commons Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales; http://creativecommons.org/licenses/by-nc-sa/2.0/uk/