Which amendment protects a defendant from being a witness to against himself?

The Fifth amendment
The Fifth amendment also protects criminal defendants from having to testify if they may incriminate themselves through testimony. A witness may "plead the Fifth" and not answer if the witness believes answering the question may be self-incriminatory.
The amendment reads:
No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury, except in cases arising in the land or naval forces, or in the Militia, when in actual service in time of War or public danger; nor shall any person be subject for the same offence to be twice put on jeopardy of life or limb; nor shall be compelled in any criminal case to be a witness against himself, nor be deprived of life, liberty, or property, without due process of law; nor shall private property be taken for public use, without just compensation.