Half Bad is a 2014 young adult fantasy novel written by English author Sally Green that won the 2015 Waterstones Teen Book Prize and was shortlisted for the 2015 Branford Boase Award. 
 On 3 March 2014, the book set the Guinness World Record as the 'Most Translated Book by a Debut Author, Pre-publication', having sold in 45 languages prior to its UK publication by Penguin books.
 Half Bad is set in modern-day Europe, mainly in Britain, where witches and humans (fains) live together. There are two primary types of witches: Blood witches (generally oppressed and written off as evil) and Fairborn witches (the main population). The 17-year-old protagonist, Nathan, is half Fairborn and half Blood, or a Half Code. His mother is dead, and his father, Marcus, is known as the most powerful and the smartest Blood witch in the world. Due his parentage, Nathan's every move is monitored by the Council of Fairborn Witches. He has to follow certain rules, but when he breaks one of them, his Gran is deemed unfit to be his guardian, and he receives a new guardian, Celia. Trapped in a cage and abused by Celia, Nathan has to escape before his seventeenth birthday, when he will receive three gifts from his family and his magical ability, or Gift. Otherwise, he will die.
 Sally Green submitted Half Bad to an agent in January 2013; in March, editorial director Ben Horslen acquired the manuscript for Penguin Books children's imprint Puffin Books, billing it "the book of the Bologna Children's Book Fair" after a 6-figure bidding war. In the run up to its publication in the UK on March 3, 2014, international rights to Half Bad sold rapidly; within 13 weeks of acquisition, it had sold in 25 territories; by November 2013, 36. Upon publication day, it broke the Guinness World Record for 'Most Translated Book by a Debut Author, Pre-publication' with 45 different translations.
 Even prior to its publication people drew comparisons to The Hunger Games, Harry Potter or the Twilight series. Half Bad has also been compared to Nineteen Eighty-Four by George Orwell. 
Additionally, Half Bad has already broken two Guinness World Records as the most translated book – and the most translated children's book – by a debut author before publication.
 A Publishers Weekly starred review states, "This grim and thrilling tale, first in a planned trilogy, features understated prose that lets readers' imaginations fill in the blanks, as well as a well-developed sense of Witch culture. Nathan, the damaged survivor of horrific abuse, is an unforgettable protagonist, and Green expertly captures his torment at being caught between the mutually hostile sides of his heritage." Kirkus Reviews states, "Green propels Nathan forward with the help of often underdeveloped secondary characters, who are overshadowed by the imaginary relationship Nathan builds with his father; it is this that keeps both Nathan and readers going." In a review for Tor.com, Kat Kennedy writes, "Sally Green's Half Bad is the perfect novel for inspiring one to despise all of humanity or fall onto the ground and weep pathetically. Needless to say, it is an excellent book." 
 In a review for The Guardian, Philip Womack writes, "While there is nothing new here, Half Bad's combination of themes will no doubt be entirely attractive to a large section of readers. Whether it will retain a hold on their imaginations is another matter." In a review for The Telegraph, Martin Chilton writes, "Half Bad doesn't always feel particularly original (scenes are set in mysterious alleys) but it is full of suspense." 
 Half Bad won the 2015 Waterstones Teen Book Prize. It was also shortlisted for the 2015 Branford Boase Award, which seeks to acknowledge outstanding debut novels for children and teenagers; it is an award presented both to the author and editor.
 Half Wild was released on 24 March 2015. The third and final book in the series, Half Lost, was released in March 2016.
 In November 2014 a Companion story, Half Lies was released.
 A feature film adaptation was announced by Fox 2000 in 2013 with Karen Rosenfelt attached, but went unproduced. Netflix announced a TV adaptation in 2020, to be helmed by Joe Barton, which was released 28 October 2022 as The Bastard Son & The Devil Himself.