The book provides an assessment of the contribution of pronoun omission to the complexity and efficiency of varieties of English and the influence of language contact on its attestation and pervasiveness. On the one hand, omitted pronouns result in simpler and more efficient structures, provided their antecedents are retrievable from the context. On the other hand, the choice between overt and omitted pronouns depends on several grammatical constraints, which in turn may entail an increase in system complexity. Two methodologically different but complementary case studies are presented, which contribute new findings to the literature at the crossroads of research on World Englishes, complexity, efficiency, and pronoun omission.