The right to represent yourself does not specifically exist in the U.S. Constitution. However, the U.S. Supreme Court has determined that you have an implied right, based on the Sixth Amendment.

Origins
In Faretta v. California, the U.S. Supreme Court acknowledged that no particular provision in the U.S. Constitution creates the right to self-representation, but that reading all of the rights in context, there is an implied right to self-representation.

You have the right to present your own defense in a criminal proceeding, and this right is unconditional provided you make a timely motion (don't wait until the last second), and you voluntarily and intelligently elect to do so.

Problems
To represent yourself is no small feat. It requires long hours of research, tedious, and often boring written motions, and a great deal of patience for the antiquated and quite formalistic evidence requirements.

Lawyers must go to school for years and pass a difficult exam before they are able to represent individuals. Those with less training and preparation are facing a difficult battle.

Limitations
A trial court may deny or limit your self-representation if there is a physical reason to do so (such as a speech impediment). Also, if you are disruptive, disobedient, or disrespectful, a court may revoke your right to self-representation.

Also, courts will severely sanction you if your desire to represent yourself is merely a pretext to stall the trial.

Old Adage
The old saying, "He who represents himself has a fool for a client," is often cited in the legal community. With few exceptions, self representation is not recommended for criminal proceedings.