The principle of proportionality is a legal principle that holds that the government's actions must be proportionate to the objectives they are trying to achieve. This means that the government cannot take actions that are more restrictive than necessary to achieve its goals.

The three elements of the principle of proportionality are necessity, proportionality, and effectiveness. Necessity means that the government's actions must be necessary to achieve its goals. Proportionality means that the government's actions must be proportionate to the objectives they are trying to achieve. Effectiveness means that the government's actions must be effective in achieving its goals.

The principle of proportionality is applied in practice by the courts, the legislature, and the executive branch. The courts weigh the necessity, proportionality, and effectiveness of the government's actions when reviewing laws and regulations. The legislature weighs the necessity, proportionality, and effectiveness of the government's actions when passing laws. The executive branch weighs the necessity, proportionality, and effectiveness of the government's actions when implementing laws and regulations.

The principle of proportionality has been applied in practice in a number of cases, including Citizens United v. Federal Election Commission, A. and B. v. the United Kingdom, and R. v. Oakes. In Citizens United, the Supreme Court held that the government's ban on corporate spending in elections was unconstitutional because it was not narrowly tailored to achieve its goal of preventing corruption. In A. and B. v. the United Kingdom, the European Court of Human Rights held that the government's policy of detaining asylum seekers was unlawful because it was not proportionate to the objective of preventing illegal immigration. In R. v. Oakes, the Canadian Supreme Court held that the government's law criminalizing possession of marijuana was unconstitutional because it was not proportionate to the objective of reducing drug use.

The principle of proportionality has been criticized for being too vague and subjective, too difficult to apply in practice, and giving too much power to the courts. Critics argue that the principle is too vague and subjective because it does not provide clear guidance on how to weigh the necessity, proportionality, and effectiveness of the government's actions. They also argue that the principle is too difficult to apply in practice because it requires judges to make complex and difficult decisions about the necessity, proportionality, and effectiveness of the government's actions. Finally, critics argue that the principle gives too much power to the courts because it allows judges to strike down laws and regulations that they believe are not proportionate to the government's objectives.