Series LevelIn general the characters on the show are older than they are in the novel. For example, Ned and Cat Stark are both supposed to be in their mid 30s in the books, having married when they were around age 18. In the show the actors who portray them are in their 50s and 40s respectively. The show also adds a couple of years between Robert's Rebellion and the events of the series and ages the child characters appropriately. Tyrion Lannister is significantly more handsome than in the novels where he's described as having eyes of different colors and mixed black and blond hair.A few names are changed in the show from the books, presumably to avoid confusion or unwanted comparisons. For example, the "White Walkers" are more commonly referred to as "The Others" in the books. Presumably this was changed to avoid comparisons with the antagonists from the tv show LOST. Theon Greyjoy's sister Yara, is named Asha in the books. This was changed to avoid confusion with the Wildling woman Osha as their names would sound virtually identical when spoken. Lysa Arryn's son Robin was named Robert in the books (named after the King). The show changed his name to Robin, so the audience wouldn't get him confused with Robert Baratheon and Robb Stark.The back-story of Lyanna Stark's death at the Tower of Joy and the promise she forced Ned to make are -eliminated from the show. While these were a significant part of Ned's back-story and the mythology of the novel, they appeared mostly in the form of Ned's internal monologues and would have been difficult to represent on screen.The show adds several sex scenes, often as cover for exposition, and invents the character of Ros, the prostitute who sleeps with a number of characters. Similarly, the show makes Littlefinger's ownership of brothels more prominent than in the novels, where they are just one of many moneymaking enterprises he owns.Season OneThe initial sex scene between Khal Drogo and Daenerys Targaryen is quite different between the novels and the show. In the novel, while Daenarys is worried that Drogo will assault her, they ultimately have consensual sex. In the show, the encounter is depicted as a rape with Drogo not seeking her consent and Daenerys weeping throughout.The show invents a couple of scenes featuring Jaime Lannister, who did not become a point of view character until the third book.The show invents a scene where Cersei visits Catelyn Stark at Bran's bedside and relates how she gave birth to a stillborn child. This was presumably done to make Cersei more sympathetic.In the book, Daenerys is said to have violet eyes. In the show her eyes are green. Executive Producers, David Benioff and Dan Weiss said they originally had Emilia Clarke wear violet contact lenses, but felt that it detracted from her performance (which is largely conveyed through the eyes) and so the contacts were discarded.Jon's direwolf, Ghost, is also completely mute in the books. In the show he whines, barks, and growls like normal dogs/wolves do. David Benioff and Dan Weiss said that originally it was scripted that Ghost was mute. However, during initial editing, they found it just didn't look/sound right having a silent dog and so they nixed the idea.Season TwoThe show is much more explicit about the sexual relationship between Renly Baratheon and Loras Tyrell, as well as the one between Stannis Baratheon and Melisandre of Asshai.The show depicts Stannis Baratheon as learning of Joffrey's bastardry from Ned Stark. In the novels, Stannis had his own suspicions about Joffrey's legitimacy. In the novels, it was Stannis who sent Jon Arryn to try and find out whether Joffrey was legitimate.Davos Seaworth is missing the fingers on his right hand on the show. In the book, he's missing the fingers on his left hand. This was done because actor Liam Cunningham is left-handed and would be more functional using his dominant hand.Talisa Maegyr does not appear in the novels. Instead, Robb weds Jeyne Westerling, daughter of Lord Gawen Westerling- an impoverished, but proud bannerman to Casterly Rock.The show invents the character of Alton Lannister to deliver Robb's peace terms. In the novels this is done by Cleos Frey who is the son of Jaime Lannister's aunt. Presumably this was done to avoid confusion since House Frey is an ally of the Starks.In the show, Osha gains Theon Greyjoy's trust by sleeping with him. In the novels she does so by demonstrating her skill with a spear.Arya's time at Harrenhall is different in the show than in the books. In the novels she serves as a common kitchen servant when Tywin is at Harrenhall. She is only elevated to cupbearer once Roose Bolton takes the castle. In the novels, Arya gives different names to Jaquen H'ghar. Instead of Tickler and Amory Lorch she gives the names of Chiswyck, a follower of Gregor Clegane who boasts of taking part in a gang rape, and Weese, the cruel head of the kitchens. She uses her third name to name Jaquen H'ghar, as in the show, but instead of enlisting his help to escape, she blackmails him into helping free a group of Northern prisoners who help take over the castle. In the novels, Amory Lorch is fed to a bear after Roose Bolton captures Harrenhall.The encounter in the House of the Undying is significantly different. In the novels, Dany goes there willingly seeking knowledge. In the show, she goes there to retrieve her dragons which have been stolen. The visions she sees are also different. In the novel she has visions of several characters who she does not recognize. However, on screen these would have been clearly recognizable to the audience and thus much of the mystery of the visions would be undermined.In the novels, Dany does not leave Xaro Xhoan Daxos for dead. Instead, he lives and makes another appearance later in the novels. However, his fate is still left ambiguous on the show and could re-appear if needed.Season ThreeIn the novels, Barristan Selmy initially comes to Danaerys disguised as "Arstan Whitebeard", an aged Westerosi serving as a squire to a warrior named Strong Belwas. He only reveals his identity towards the end of the third novel, explaining that he had wanted to observe Danaerys and discern what type of Queen she was before offering his services. This was likely changed because in the book, it could be a surprise to the reader when his identity was revealed. In the show, people would immediately know who he was or possibly be confused and think it was the same actor playing a different role.In the novels Robb does not plan to attack Casterly Rock. Instead, Robb gets word that the Ironborn are invading the North and decides to take most of his forces home to defend his people. This explains why most of the Stark forces are at the Twins for Edmure's wedding since the Twins are on the way to the North but not Casterly Rock.In the novels neither Brynden "Blackfish" Tully or Robb's queen are present at the Red Wedding.Gendry's role is expanded in the show. In the novels he is not kidnapped by Melisandre. Instead she intends to sacrifice Edric Storm, King Robert's only acknowledge bastard.In the novels it is not Locke who cuts off Jaime's hand but rather Vargo Hoat, a mercenary originally hired by Jaime's father who switches sides and joins Roose Bolton.Tormund Giantsbane is portrayed differently in the show than in the novels. In the show he leads the Wildling raid south of the Wall and is openly hostile to Jon. In the book Tormund is very friendly with Jon and stays north of the Wall. Instead it is another Wildling, Styr the Magnar of Thenn, who leads the raid and who is suspicious of Jon's motives.In the novels we do not see any of Theon's torture at the hands of Ramsay Snow, just the aftermath of it.In the show, the first man who Arya kills is a Frey soldier who she hears bragging about taking part in the Red Wedding. In the show she had already killed several people by that point. Though the first person she ever killed is the same in the show and the book, that being a stable boy who tried to stop her from escaping from King's Landing.In the novels the slaves in Slaver's Bay are mostly depicted as being white, the same as their masters. Very few, if any, are said to be from the Summer Islands, the region where black people are from in the novels. In the show, the slaves are generally depicted as black or dark skinned. This causes the "Mhysa" scene with Danaerys at the end of season 3 to have unfortunate real world racial connotations.Season FourIn the books, Jaime and Brienne arrive at King's Landing after Joffrey is already dead.The show is much more explicit about Oberyn Martell's bisexuality while the books strongly hint at it.While most of the action in season four comes from the third book, they do add in some of the plotlines of Bran and Theon from the fifth book.In the books Theon's sister does not attempt to rescue him from the Boltons.In the books, Jaime and Cersei's sexual encounter in the sept is depicted as consensual. In the show, the scene is more ambiguous, leading many to view it as Jaime forcing himself on Cersei.In the books it is Donal Noye, the blacksmith of Castle Black, who organizes the defenses against the Wildlings.In the book, Jaime secretly trains in sword fighting with Ser Ilyn Payne, who is discreet about it because he has no tongue. In the show, Jaime secretly trains with Bronn, who is discreet about it because he's paid to be. This was likely to allow some more dialogue and exposition and possibly just to give Bronn more screen time.Tyrion's escape is significantly different in the books. In the books, Jaime admits to having lied about Tysha, Tyrion's first wife, who their father forced him to put aside. Jaime had originally told Tyrion that Tysha, who they had apparently saved from brigands on the road, was actually a prostitute who Jaime had hired so that Tyrion could lose his virginity. This is the story which Tyrion tells Shae and Bronn in season one. In the books, Jaime admits that this was a lie he had created to spare Tyrion's feelings and that Tysha had really loved Tyrion. Angered at this revelation, Tyrion tells Jaime about Cersei's serial infidelity to him and then goes to their father's chamber to confront him over a lifetime of betrayals. In the show, Shae draws a knife on Tyrion and Tyrion strangles her in self defense. In the books, Shae instead pleads for her life upon seeing Tyrion and he strangles her in cold blood. Also in contrast to the show, where Tyrion immediately apologizes for killing her, Tyrion in the books seems to show no regret for killing Shae. The confrontation between Tywin and Tyrion is largely the same but in the books it is Tysha who Tywin refers to as a "whore", which prompts Tyrion to kill him.