Addressing the central role of variation in human language, this book examines how it operates across multiple structural levels, integrating empirical case studies of change in the lexicon, word classes, constructions, style, and sociolinguistic dimensions.Drawing on large-scale corpus data, the volume analyses competition among word forms, shifts in grammatical categories, changes in constructions, stylistic differentiation, and language use in relation to gender and social values. It shows how linguistic choices emerge from interacting structural, semantic, and social factors, producing patterns of variation. Using quantitative and computational methods implemented in R and Python, the studies demonstrate how empirical evidence illuminates language use and its role in shaping linguistic systems. Together, these analyses argue that variation is fundamental to linguistic organization.This book will be of interest to researchers and students across linguistics, particularly those working in corpus linguistics, cognitive linguistics, sociolinguistics, and computational linguistics, especially those concerned with language variation and change.