This book explores how recursion—our ability to embed structures within structures—shapes human language. Bridging theory and experiment, it highlights two forms of recursion: direct recursion, which merges items directly, and indirect recursion, which embeds items within each other, showing that indirect recursion is sometimes treated as direct recursion in initial stages in acquisition. Drawing on cross-linguistic data from English, Mandarin, Hungarian, Romanian, Tamil, and other languages, the book reveals both universal patterns and language-specific variation in recursive structures such as recursive possessives, prepositional phrases, adjectives, and relative clauses. Ideal for students and researchers in linguistics, the book integrates fresh insights from theoretical linguistics, psycholinguistics, and biolinguistics to provide a comprehensive view of how recursion is structured, acquired, and processed across languages.