One major theme of Bud, Not Buddy is the importance of family. Bud spends most of his short life focused on family. Before his mother dies, he is very close to his mother, and she is really the only person in his life. After she dies, he becomes obsessed with finding the man in the fliers, the man he assumes is his father. When Bud's life is unpleasant, when he is being hurt both emotionally and physically, he determines that the only way to stop this pain is to find his family.
When Bud finds Herman E. Calloway, he is disappointed because his imagination has drawn up a man much different from the one he meets. This man is old and gruff and mean. But as time goes on, Bud - and the reader - learns that the old man is gruff and mean and unhappy because he lost the person who really meant something to him - his daughter, or his family. The author portrays the importance of family in both Bud's and Herman Calloway's inability to be happy or fulfilled without family. But when they find out they are truly related, Bud's life turns around, and Herman E. Calloway cries and mourns his daughter. Both men are now able to understand the importance associated with family.
The importance of family is also portrayed through the other relationships that Bud develops throughout the story. For example, his 'pretend family' that helps him get food at the soup kitchen are not 'real' family, but they become like family to Bud. The kindness they show him makes him feel like they could be family. Miss Thomas, the singer in Herman E. Calloway's band, becomes family to Bud because she cares about him. She is concerned for both his well-being and for Herman's well-being. Bud learns that conventional family is not the only type of family one can have, but rather family is made up of those people who care about us.