Differential Object marking (DOM), a linguistic phenomenon in which a direct object is morphologically marked for semantic and pragmatic reasons, has attracted the attention of several subfields of linguistics in the past few years. DOM has evolved diachronically in many languages, whereas it has disappeared from others; it is easily acquired by monolingual children, but presents high instability and variability in bilingual acquisition and language contact situations. This edited collection contributes to further our understanding of the nature and development of DOM in the languages of the world, in acquisition, and in language contact, variation, and change. The thirteen chapters in this volume present new empirical data from Estonian, Spanish, Turkish, Korean, Hindi, Romanian and Basque in different acquisition contexts and learner populations. They also bring together multiple theoretical and methodological perspectives to account for the complexity and dynamicity of this widespread linguistic phenomenon.