Book excerpt: This book explores what identity is, what factors contribute to it, how it develops, and the impacts that a strong or weak sense of self can have on a person's health, happiness, and future. Many teens grapple with the seemingly simple question, "Who am I?" and struggle to integrate their experiences at school, at home, and with friends into their burgeoning sense of identity. How teens see themselves can influence the friends they choose, the decisions they make, and their mental and physical well-being. Having a strong sense of self can help them resist peer pressure, avoid risky behaviors, and make choices and plans that align with their values and interests. Yet research shows that such factors as heavy social media use can have a strongly negative effect on healthy identity formation for today's teens. Who Am I? Understanding Identity and the Many Ways We Define Ourselves examines the subjects of identity and identity formation across the lifespan, with special emphasis on the teenage years. Beyond simply discussing relevant psychological theories, the book focuses on how identity formation happens in the real world and how it affects the daily lives of teens. It also includes a collection of fictional case studies that provide concrete, relatable illustrations of concepts discussed in the book.