This comprehensive comparison of the two Ibero-Romance languages, Spanish and Portuguese, primarily focusing on their European varieties, sheds light on the numerous convergences as well as divergences of these closely related idioms and their shared history. The language comparison encompasses phonology, morphology, syntax, and lexicon. The synchronic analysis is supplemented by extensive notes on the historical development, with dedicated chapters on external and internal language history rounding out the presentation of historical developmental stages. The study also examines the diasystematic branching of both languages, the results of centuries of language contact, and the current situation of their distribution worldwide. Additionally, the typological differences that have emerged throughout the language development are highlighted.