Living wills (also called advance directives or advance decisions in UK) specify your medical preferences if you become unable to communicate. Most adults don't have one despite the genuine need — accidents, severe illness, dementia all leave families guessing without it.
What it covers
Specific medical treatments you would or wouldn't want. Resuscitation preferences. Organ donation. End-of-life care preferences. Who can make medical decisions for you (covered separately in Health and Welfare LPA).
How to create one
Compassion in Dying (UK charity) provides free template. Solicitor for complex situations. Discuss with family before signing (they need to know your wishes). Provide copy to GP and family members.
Twenty minutes of paperwork; profound benefit to family in difficult moments. Most adults assume they'll have time later; circumstances don't always cooperate.