Perjury takes place when a person willfully swears a false oath, or tells a lie instead of the truth when making a solemn declaration instead of an oath, and this lie is going to make a difference in the outcome of a court trial. It does not matter if the lie was spoken aloud, or was in writing. Perjury is considered to be quite the serious offence. Federal law in the USA does not treat those who commit perjury kindly at all. It considers perjury a felony, and recommends a prison term of up to five years. In the UK, a person who commits perjury can receive a prison sentence of up to seven years. Perjury rules are also valid when a person signs a document that states up front that they are signing “under penalty of perjury.” United States income tax forms contain this statement. In order for a person to actually be convicted of the crime of perjury, it must be proven that the perjury was done deliberately. This is not always easy to do.