"Judy Moody Was in a Mood" is a children's book by Megan McDonald that follows the adventures of a third-grade girl named Judy Moody. In this story, Judy experiences a variety of emotions, particularly when she feels grumpy and frustrated. Her mood affects her interactions with friends and family, leading to humorous situations. Throughout the book, Judy tries to change her mood by engaging in different activities and challenges. She learns valuable lessons about friendship, self-expression, and the importance of understanding one's feelings. The story is relatable for young readers, making it a popular choice for early chapter book readers.