An official language is a language that is specifically designated to be so in the constitutions of countries, states, and other territories. (States and areas without a constitution, by this definition, lack official languages.)
Half the countries in the world have official languages. Some have only one official language, such as Albania, France (although there are more native languages in France) or Germany. Some have more than one official language, as Belgium, Finland, Afghanistan, Paraguay, Bolivia, India, Switzerland and South Africa.
In some countries, such as Iraq, Italy and Spain, there is an official language for the country, but other languages are co-official in some important regions. Some countries, such as the United States, have no official languages, but there are official languages in some US states (See Languages in the United States). Finally, some countries have no official languages, such as Australia, Eritrea, Luxembourg, Sweden or Tuvalu.
As a consequence of colonialism and/or neocolonialism, in some countries in Africa and in the Philippines the official and learning languages (French or English) are not the national languages or the most widely spoken. In contrast, as a consequence of nationalism, in the Republic of Ireland what is the state's official national language (Irish) is actually spoken by only a small proportion of people, while the language given secondary inferior legal status (English), is actually the spoken language of the majority. A similar situation occurs in New Zealand, where English is the day-to-day language of the vast majority of the population, but its only official language is Maori.
In some countries, the issue of which language is to be used in what contexts is a major political issue. There is a list of such countries.