The study of composition operators forges links between fundamental properties of linear operators and beautiful results from the classical theory of analytic functions. This book provides a self-contained introduction to both the subject and its function-theoretic underpinnings, and features a development accessible to anyone who has studied basic graduate level real and complex analysis. The work traces how such operator-theoretic issues as boundedness, compactness, and cyclicity, when studied in the context of composition operators, evolve into questions about subordination, value-distribution, angular derivatives, iteration, and functional equations; and it carefully develops each of these classical topics.

0 Linear Fractional Prologue.- 0.1 First Properties.- 0.2 Fixed Points.- 0.3 Classification.- 0.4 Linear Fractional Self-Maps of U.- 0.5 Exercises.- 1 Littlewood's Theorem.- 1.1 The Hardy Space H2.- 1.2 H2 via Integral Means.- 1.3 Littlewood's Theorem.- 1.4 Exercises.- 1.5 Notes.- 2 Compactness: Introduction.- 2.1 Compact Operators.- 2.2 First Class of Examples.- 2.3 A Better Compactness Theorem.- 2.4 Compactness and Weak Convergence.- 2.5 Non-Compact Composition Operators.- 2.6 Exercises.- 2.7 Notes.- 3 Compactness and Univalence.- 3.1 The H2 Norm via Area Integrals.- 3.2 The Theorem.- 3.3 Proof of Sufficiency.- 3.4 The Adjoint Operator.- 3.5 Proof of Necessity.- 3.6 Compactness and Contact.- 3.7 Exercises.- 3.8 Notes.- 4 The Angular Derivative.- 4.1 The Definition.- 4.2 The Julia-Carathéodory Theorem.- 4.3 The Invariant Schwarz Lemma.- 4.4 A Boundary Schwarz Lemma.- 4.5 Proof that (JC 1) ?(JC 2).- 4.6 Proof that (JC 2) ?(JC 3).- 4.7 Angular derivatives and contact.- 4.8 Exercises.- 4.9 Notes.- 5 Angular Derivatives and Iteration.- 5.1 Statement of Results.- 5.2 Elementary Cases.- 5.3 Wolff's Boundary Schwarz Lemma.- 5.4 Contraction Mappings.- 5.5 Grand Iteration Theorem, Completed.- 5.6 Exercises.- 5.7 Notes.- 6 Compactness and Eigenfunctions.- 6.1 Königs's Theorem.- 6.2 Eigenfunctions for Compact C?.- 6.3 Compactness vs. Growth of ?.- 6.4 Compactness vs. Size of ? (U).- 6.5 Proof of Riesz's Theorem.- 6.6 Exercises.- 6.7 Notes.- 7 Linear Fractional Cyclicity.- 7.1 Hypercyclic Fundamentals.- 7.2 Linear Fractional Hypercyclicity.- 7.3 Linear Fractional Cyclicity.- 7.4 Exercises.- 7.5 Notes.- 8 Cyclicity and Models.- 8.1 Transferenc from Models.- 8.2 From Maps to Models.- 8.3 A General Hypercyclicity Theorem.- 8.4 Exercises.- 8.5 Notes.- 9 Compactnessfrom Models.- 9.1 Review of Königs's Model.- 9.2 Motivation.- 9.3 Main Result.- 9.4 The Hyperbolic Distance on U.- 9.5 The Hyperbolic Distance on G.- 9.6 Twisted Sectors.- 9.7 Main Theorem: Down Payment.- 9.8 Three Lemmas.- 9.9 Proof of the No-Sectors Theorem.- 9.10 Exercises.- 9.11 Notes.- 10 Compactness: General Case.- 10.1 Motivation.- 10.2 Inadequacy of Angular Derivatives.- 10.3 Non-Univalent Changes of Variable.- 10.4 Decay of the Counting Function.- 10.5 Proof of Sufficiency.- 10.6 Averaging the Counting Function.- 10.7 Proof of Necessity.- 10.8 Exercises.- 10.9 Notes.- Epilogue.- References.- Symbol Index.- Author Index.