There are three types of articles in English: indefinite articles (a, an), the definite article (the), and no article. The choice of article depends on whether the noun refers to a specific or non-specific thing. Rules govern the use of "a" versus "an" based on whether the following word starts with a vowel sound, and whether modifiers like adjectives are used. The definite article is often omitted for geographical locations, languages, sports, and academic subjects.