The 6th Amendment to the Constitution of the United States guarantees a criminal defendant the right to have the assistance of legal Counsel for his defense, or a criminal defense lawyer. A criminal defense lawyer is an expert in defending individuals or companies that are charged with any variety of crime.

A Philadelphia criminal defense lawyer deals mostly with ensuring that the apprehension of his or her client, the searching of a client's person and property, and arrest are all in accordance and within the bounds of the client's 4th Amendment rights. A criminal defense lawyer also advises his or her client on any statements the client should or should not make, under their 5th Amendment rights, and represents his or her client's best interests in a criminal trial.

It is the policy in the United States that all criminal defendants are entitled to be presumed innocent until proven guilty beyond a reasonable doubt of each point of the alleged crime. It is the duty of a criminal defense lawyer to make sure that the judge and the jury in a criminal case question every element of the accusation against his or her client, and introduce the possibility of doubt. It is not the responsibility of a Philadelphia criminal defense lawyer to prove that any client is innocent, only that the client's guilt is doubtful.

Because most serious crimes in the U.S. are tried before a jury of twelve individuals and all twelve must be unanimous in a verdict to convict or acquit the defendant, a criminal defense lawyer will make every effort to convince the jury of the questionable reliability of accusations and witnesses against the defendant. Philadelphia criminal defense lawyers pursue their client's cause aggressively through every stage of a criminal prosecution.

Many criminal defense lawyers are employed by the government and are referred to as "Public Defenders." These criminal defense lawyers are often fresh out of law school and are looking to get a lot of courtroom experience before embarking on other careers, but some Philadelphia criminal defense lawyers are experienced experts who make criminal defense their permanent avocation.

Even though Philadelphia criminal defense lawyers usually become extremely wealthy few people choose to become criminal defense lawyers because of the high stress nature of the job, claims on conscience, and the potential responsibility for a client spending years in prison, or even being executed. It takes a certain type of person to be a successful Philadelphia criminal defense lawyer for a long period of time, and to actually enjoy it.