We introduced our first edition of this book with the statement that ‘our understanding of the genetics of common diseases has come a long way in recent years’. That statement is as true now as it was then but even we could not have foretold the enormous strides being made in the genetics of all the common diseases, with stroke being an exemplar of the complexity and struggles of that science. The advances in our mathematical and statistical capabilities along with the strides in genetic laboratories and, just as importantly, the reduction in manufacturing cost of microarray chip technology have all helped in greatly improving our understanding of stroke genetics. Many thousands of willing patients have agreed to donate their DNA in the hopes of benefitting future generations. Researchers have meticulously and painstakingly compared and contrasted millions of human polymorphisms. The enormity of this task should not be underestimated. The gratifying popularity of our first edition prompted the publishers to encourage us to produce a second edition. We approached our colleagues from across the continents, and despite their hectic schedules, not one hesitated in responding to our call.