What is longevity? The dictionary has it as living to a great age, but there's another meaning - if something has longevity, it has constancy and persistence, for much as long life itself is great, it's not as useful a goal as a good, abundant and durable life. This book is about what we can do to live better for longer; it's about expanding our 'health span' and enhancing wellbeing with each year that passes.