Regular expressions (regex) in Python are implemented through the re module, which provides pattern matching and text manipulation capabilities. Regex patterns define search templates that can match, extract, replace, or validate text based on character sequences, metacharacters, and quantifiers. Understanding regex is fundamental for data cleaning, validation, parsing, and text processing tasks across web scraping, log analysis, and input sanitization. The key mental model: think of regex as a mini-language for describing text patterns—each symbol adds a rule about what to match, and the engine tries to satisfy all rules simultaneously.