The themes of identity and change run throughout Criss Cross in many ways. Most immediately, this is primarily a novel about teenagers, and each of the young people in the novel finds himself or herself changing, often by the moment. As a result, everyone is continually asking, “Who am I?” in different ways. The author comments on change through the stylistic aspects of the novel, often shifting styles to match a chapter’s focus. However, the characters often reflect on the potential for change themselves. The novel’s first line is, “She wished something would happen,” and once Debbie is done defining and hedging that wish, which changes as soon as it comes into her mind, a second chapter begins. Hector, the male lead, tries out different metaphors for himself, consciously considering if the metaphor of childhood as cocoon was appropriate for him and if he is emerging as a butterfly (he decides he is not). Other characters are shown to be as confused about identity as well. Dan Persik is explicitly said to be under a magic spell and readers are told, “He wasn’t really a donkey” even as a drawing shows Dan with a donkey’s head. Which is real, the appearance or the statement? The inside or the outside? The person you used to be or the person you’re becoming? Everyone in the novel, from the parents to the senior-citizen neighbors, wrestles with these questions.

What sets Criss Cross apart from many other novels—young adult or otherwise—is that the characters neither exist nor change in isolation. Instead, like elements in a mosaic, they take on a major portion of their identity from the other pieces of their community they are placed next to. This positional quality is brought home in many ways. For example, Hector’s sister’s face appears beside his in the mirror, demanding comparison to the parallel columns, and Chapter 22 follows two characters through independent but parallel strands of story by placing two columns of text side by side. This theme is made most explicit, however, though the radio show that gives the novel its name: "Criss Cross." The show itself juxtaposes odd or surprising songs and comments to produce humor, and the teens in the novel listen to it sitting side by side in a truck. The nature of this situation changes radically depending on who is there; it is a very different thing to listen to a radio show in the dark as part of a group of four versus to listen to it alone in the dark as part of a pair that might become a couple.

Juxtaposition creates serendipity. Nothing just happens and then is forgotten in Seldem. Instead, each seemingly casual event links together. If two things happen next to each other in time, space, theme, or even design (as happens in the haiku chapter or the chapter in which Debbie and Patty are reduced to initials, then to question marks), they will relate. What is more, even the smallest interaction can produce tremendous change. In Chapter 10, Debbie and Patty comment on this, referring to the butterfly effect, a popular chaos theory explaining how distant and seemingly tiny acts can have great influence, like a butterfly flapping its wings in Indonesia can create tidal waves in Florida. In Criss Cross, the defining small detail is the open clasp on Debbie’s necklace, which allows it to slip loose and travel through the community, ideally to link Debbie and Hector.

Everyone desires intensely in Criss Cross. They are not always sure what they want, but they want. From Debbie’s desire for something to happen that opens the novel to Hector’s desire to learn to play the guitar to the various romantic wishes and longings that possess most of the characters, Criss Cross is filled with desire. This throbbing desire is wound together with the themes: people’s desires change them, and their desires change when they do. People feel and recognize new desires when they are placed close to someone or something new, and this changes them in turn, and so on.