This question can be explored from several perspectives—for instance, by examining the objects of study, the fundamental questions being asked, or the instruments used in research. Particle physics can also be understood by contrast, through comparison with other natural sciences. These various approaches are presented in this chapter. Of course, the wide range of topics in particle physics can only be briefly introduced here, but they will be revisited and explored in greater depth throughout the book. We hope this chapter serves as an invitation to embark on an exciting journey—one that leads not only to profound insights but also to the many open questions at the heart of modern nuclear and particle physics.