The Hay Festival is marking its 30th anniversary by "crowd sourcing" a list of the world's most essential books.
The #Hay30Books names so far include 2013's Wales Book of the Year winner Pink Mist from poet Owen Sheers.
The festival has chosen the first 15 books from mostly recent years but is asking readers to pick the others dating back to the first event.
Its birthday in May will also see 30 schools plant trees over 30 acres in a partnership with the Woodland Trust.
The border town of Hay-on-Wye in Powys, well known for its second hand book shops, has hosted the annual literary event since the spring of 1987.
Festival director Peter Florence said "sharing stories" had been key to Hay's success.
"Fundamentally the festival is about sharing stories and sharing ideas, and our audience is the most incredible resource," he said.
The starting 15 for #Hay30Books
The first books chosen range from poetry and politics to children's fiction, award-winning novels, nature and evolutionary biology.
- Kid by Simon Armitage (1992)
- Dr Tatiana's Sex Advice to All Creation by Olivia Judson (2002)
- Chronicles of Ancient Darkness series by Michelle Paver (2004)
- Half of a Yellow Sun by Chimamanda Ngozi Adichie (2006)
- Finding Violet Park by Jenny Valentine (2007)
- A Golden Age by Tahmima Anam (2007)
- The Road Home by Rose Tremain (2007)
- Sum: Forty Tales from the Afterlives by David Eagleman (2009)
- Oblivion: A Memoir by Héctor Abad (2010)
- How To Train Your Dragon series by Cressida Cowell (2010)
- The Old Ways: A Journey on Foot by Robert Macfarlane (2012)
- Far from the Tree: Parents, Children and the Search for Identity by Andrew Solomon (2012)
- Pink Mist by Owen Sheers
- Between the World and Me by Ta-Nehisi Coates (2015)
- Headscarves and Hymens by Mona Eltahawy (2015)
People can pick their favourite book of the last 30 years - and say why in under 30 words - via Twitter, Facebook or Instagram using the hashtag #Hay30Books.
Mr Florence said: "In those 30 years, the world has changed so much, it's almost unrecognisable and yet life, love and death still seem the same and you still need people to write about them and tell stories about them."
He told BBC Wales that they were looking for people's essential books published over the last 30 years.
"Which books would you want to share with people? Our audience is the most incredible resource, they know stuff and care about stuff and have their passions, favourites and their enthusiasms and we want to tap into that and say - these are some of our discoveries, what are yours?"
The full programme for the two-week festival, which runs from 26 May, will be released in early April but early bookings include Garry Kasparov, Tracy Emin, 2016 Man Booker Prize winner Paul Beatty and Ken Dodd.
Writers and thinkers will also be asked to imagine 30 global reformations, to mark 500 years since Martin Luther signalled the start of the Protestant religious reformation.