There are thirteen people who Hannah Baker sent tapes to before her suicide. In the tapes she mentions the reasons why she holds each individual responsible for her death. The thirteen people she names in the tapes are:
Justin, who is first. Hannah had a crush on him and they kissed once but Justin went around and bragged to his friends that they did more than just kiss. This gave her a bad reputation and everyone believed that she was a slut.
Alex then receives the tapes. He spoiled their friendship by publishing a "hot or not" list of the girls in their class. He gave Hannah the title of "Best Ass" which just gave credence to her slut reputation.
Jessica is the third one to get the tapes. She was jealous of Hannah for the comparison made in the "hot or not" list. As a result, she slapped Hannah and ended their friendship. Hannah was left with a scar on her forehead as a result of the assault.
Person number four is Tyler who was a classmate who did work as a photographer for the yearbook. Hannah suspected that Tyler was taking photo's of her through her bedroom window and asked a classmate, Courtney, to help her catch Tyler red-handed.
Courtney is the fifth person to receive the tapes. She offended Hannah by spreading a rumor about sexual massages she and Hannah had given each other in Hannah's bedroom. The rumor obviously further worsened Hannah's reputation as a tart.
The sixth recipient is Marcus. He thought that the rumors about Hannah being loose were true and he tried to take advantage of her because of them.
Zach is seventh in line. He tried, on a challenge, to comfort Hannah after Marcus had left her. When Hannah did not respond to his efforts, he took notes of encouragement from her as revenge.
Ryan becomes the eighth person to receive the tapes. He gained Hannah's trust and then stole a poem, in which she detailed her personal problems, from her. He then had the poem secretly published in the school newspaper but some of their classmates realized that it was Hannah's and made fun of her about it. Hannah blamed Ryan for making her feel that even something as private as her own thoughts were not safe from inspection.
Clay is the ninth person to receive the tapes. Hannah does, however, apologize to him for he did not make her feel like committing suicide. She acknowledges that he was the nicest person she had ever met.
Justin receives the tenth tape. Hannah was hiding in a closet when she saw an unnamed classmate being raped. She blames Justin for the event since he knew about the atrocity and allowed it to happen.
Jenny will be the eleventh one to receive a tape. She was a cheerleader who had offered Hannah a lift home from a house party and had hit a stop sign during their journey. Jenny did not tell the police about the incident which led to a car accident in which one of their classmates was killed.
Bryce should be the twelfth person to receive a tape. He had sexually assaulted Hannah.
The thirteenth person who will be receiving a tape should be Mr Porter, the school counselor. When she consulted him, she secretly recorded their conversation in which she told him that she felt suicidal. Mr Porter was overwhelmed and could not help her. He, instead, told her that if she did not want to lay charges against Bryce, she should make an attempt to move on and forget about it.