Structural Additive Theory Nestled between number theory combinatorics algebra and analysis lies a rapidly developing subject in mathematics variously known as additive combinatorics additive number theory additive group theory and combinatorial number theory. Its main objects of study are not abelian groups themselves but rather the additive structure of subsets and subsequences of an abelian group i.e. sumsets and subsequence sums. This text is a hybrid of a research monograph and an introductory graduate textbook. With few exceptions all results presented are self contained written in great detail and only reliant upon material covered in an advanced undergraduate curriculum supplemented with some additional Algebra rendering this book usable as an entry level text. However it will perhaps be of even more interest to researchers already in the field. The majority of material is not found in book form and includes many new results as well. Even classical results when included are given in greater generality or using new proof variations. The text has a particular focus on results of a more exact and precise nature results with strong hypotheses and yet stronger conclusions and on fundamental aspects of the theory. Also included are intricate results often neglected in other texts owing to their complexity. Highlights include an extensive treatment of Freiman Homomorphisms and the Universal Ambient Group of sumsets A+B an entire chapter devoted to Hamidoune’s Isoperimetric Method a novel generalization allowing infinite summands in finite sumset questions weighted zero sum problems treated in the general context of viewing homomorphisms as weights and simplified proofs of the Kemperman Structure Theorem and the Partition Theorem for setpartitions. . 1. Abelian Groups and Character Sums 2. Introduction to Sumsets 3. Simple Results for Torsion Free Abelian Groups 4. Basic Results for Sumsets with an Infinite Summand 5. The Pigeonhole and Multiplicity Bounds 6. Periodic Sets and Knesers Theorem 7. Compression Complements and the 3k–4 Theorem 8. Additive Energy 9. Kempermans Critical Pair Theory 10. Zero Sums Setpartitions and Subsequence Sums 11. Long Zero Sum Free Sequences over Cyclic Groups 12. Pollards Theorem for General Abelian Groups 13. The DeVos–Goddyn–Mohar Theorem 14. The Partition Theorem I 15. The Partition Theorem II 16. The Ψ Weighted Gao Theorem 17. Group Algebras 18. Character and Linear Algebraic Methods 19. Character Sum and Fourier Analytic Methods 20. Freiman Homomorphisms Revisited 21. The Isoperimetric Method 22. The Polynomial Method Index.