The Fifth Amendment of the United States Constitution was drafted with the intention of protecting citizens from being compelled to incriminate themselves. When someone invokes this privilege, it is said that he is electing to “plead the Fifth.” The Fifth Amendment applies only to situations where the incriminating evidence is testimonial in nature. The person must expressly assert the privilege in the appropriate situation. If he does not assert the privilege when compelled to testify in one situation, he waives his right to do so in any later occurrence where he is asked to testify regarding the same matter.
In order for the Fifth Amendment privilege against self-incrimination to apply, the situation must call for the person to incriminate himself in a manner that is testimonial in nature. For example, if a person is called in front of a grand jury to offer testimony regarding an illegal transaction he made, he may plead the Fifth in order to avoid making incriminating statements. It does not have to be a court setting for the Fifth Amendment to apply; the person may assert the privilege if he is asked to testify at a congressional hearing as well. It does not, however, apply to non-testimonial forms of self-incrimination, such as urine tests or fingerprints.
In order to plead The Fifth, the person must expressly state that he is not willing to testify, as it will result in he making self-incriminating statements. He may assert the privilege while on the witness stand or simply refuse to testify in a case where he is a criminal defendant. The judge may not compel him to testify as long as there is a reasonable chance that he will make a self-incriminating statement.
If someone fails to assert this privilege in any proceeding, he may not later assert it when asked to testify on the same matter. For example, if a person testifies in a trial about how he purchased drugs from the defendant, he may not later refuse to do so while on the stand for his own trial for possession of the same drugs. Once a person testifies on any matter, he waives his Fifth Amendment rights going forward.