This volume explores the current state of Spanish sociolinguistics and its contribution to theories of language variation and change, from both synchronic and diachronic perspectives. It offers original analyses on a variety of topics across a wide spectrum of linguistic subfields from different formal, experimental, and corpus-based standpoints. The volume is organized around six thematic sections: (i) Cutting-edge Methodologies in Sociolinguistics; (ii) Bilingualism; (iii) Language Acquisition; (iv) Phonological Variation; (v) Morpho-Syntactic Variation; and (vi) Lexical Variation. As a whole, this collection reflects an array of approaches and analyses that show how in its variation across speakers, speech communities, linguistic contexts, communicative situations, dialects, and time, the Spanish language provides an immense wealth of data to challenge accepted linguistic views and shape new theoretical proposals in the field of language variation and change.