Complex plasmas are a modern research area in plasma science. Such plasmas differ from conventional high-temperature plasmas in several ways (1) they may contain additional species, including nanometer- to micrometer-sized particles, negative ions, molecules, and radicals and (2) they exhibit strong correlations (e.g., dusty plasmas) or quantum effects. Numerous applications of particle-containing plasmas and microplasmas are already emerging. This chapter provides an introduction into the field of complex plasmas and an outline on the chapters of this book.