Most countries have classes of organization or individual which they deem to be exempt from normal taxation. These vary from country to country. It is often the case that charitable organizations are exempted from tax. The definition of what constitutes a legitimate charity is open to debate and usually there will some government agency set up to make judgements about this and to monitor the conduct of the charitable organizations.
In addition, it is very common that religious institutions are exempted from tax. Naturally, this gives rise to the question of what constitutes an actual religion which, in some cases, is not always clear. The tax exemption given to organizations such as charities or religious institutions may carry with it certain obligations too. For example, tax exemption may be a requirement that the organizations refrain from political campaigning.
It is also common for educational institutions such as schools and universities to be exempted from tax. In some countries, some or all of the employees of the government or of other governments may be exempted from tax.
In the case of sales or value added taxes, many countries declare certain types of good to be exempt from the tax. For example, it is common for books to be declared free of such taxes.