The ability to make decisions and take actions that influence our life is critically important and ranges from simple everyday choices about what to have for breakfast, to far-reaching decisions about health care, personal or financial matters. When our ability to make our own decisions is impaired, whether due to dementia, learning or intellectual disability, mental illness or brain injury, that might mean we are not able to make decisions for ourselves. So, there is a need for clear assessment processes to help decide whether someone has the capacity to make their own decisions, who should make decisions on their behalf, and on what basis such decisions should be made. The guidance in this book has been written to serve the needs of doctors, lawyers, health professionals, families and whanau. It was written by experts from a range of disciplines including law, medicine and ethics, and is based on the Toolkit for Assessing Capacity. It combines an explanation of the law, case studies and practical guidance for health and legal professionals about capacity, how it is assessed, and what supporting people with impaired capacity means in practice.