Experts by Experience in the context of mental health are those who have personal experience of using, or caring for someone who uses, mental health and social care services. How do people with lived experience of mental illness contribute to scientific knowledge and personal growth? This volume comprises three distinct philosophical perspectives focused on specific theoretical and practical challenges for theorizing expertise by experience in philosophical mental health research: the idea of subjectivity in 'lived experience' and the issue of scientific validation, the prospects of shared meaning-making and the problem of injustice in 'co-production', and the philosophical role of values in navigating difference and value disagreement in psychiatry.