This document provides an introduction to genre theory and discusses some of the key challenges in defining genres. It notes that while genres are commonly used to categorize different types of texts, there is no consensus on how to define genres or determine their boundaries. Generically classifying texts involves theoretical difficulties as genres often overlap and individual texts can belong to multiple genres. The document examines debates around whether genres exist objectively or are social constructions, and if they are defined by shared content, form, or both. It also explores how genres are not fixed but change over time as new hybrid genres emerge.