What does an atheist swear on before giving testimony in court? Would you put less faith on their testimony if they didn't swear on the Bible? If not, then why does anyone swear on the Bible?

I can't comment on any other country's legal practices, but in the United Kingdom an atheist would make a Solemn Declaration instead of an oath and there would be no book involved. Members of religions other than Christianity have the right to take the Oath on the Holy Book of their particular religion.

A person's character determines whether they will tell the truth. As a juror I'd be unlikely to know the person's religious affiliation or lack thereof, and I also wouldn't know the person's character. If they didn't want to swear on a bible that wouldn't sway me. I'd be swayed by the believability of their testimony - whether it seemed truthful with respect to other facts presented and the scenario under discussion. People are no less likely to lie just because they put their hand on a bible. It's a long-standing tradition that witnesses swear on a bible and invoke God in court, a holdover from theocratic societies, but it isn't a requirement in American courtrooms. I think it's meant to formalize the solemnity and importance of the testimony.

If swearing on the bible were a religious thing, then I'd put less faith in their testimony if they DID swear on the bible. I mean, they don't believe in God but here they are swearing to him? Wouldn't that be perjury?

I've been sworn into court (more times than I'd like to admit) and they never even used a bible. I was just asked to raise my right hand and swear to the court something or another about telling the truth. They DID say "Do you swear to tell the truth, the whole truth, and nothing but the truth sohelpyougod?" and I said "I do", but I didn't really need god to help me that day so I just ignored that part.

I don't think anyone swears on the bible anymore, it appears from watching court proceedings on TV, that you are just asked to raise your right hand and "solemnly swear"

Not just atheist object to the taking of oaths or swearing on the Bible. Quakers are another group that does not. Oaths taken when testifying in court are a long legal tradition. It is not the pain of damnation but the pain of the crime of perjury that is a motivator.

As for me, if I saw someone come to court who was clearly not a believer swear on a Bible to be truthful in their testimony I might be more inclined to think they were lying.

Here is some information from the most supreme legal document in the United States.

The Presidential oath of office is described in Article II, section 1 of the Constitution:

Before he enter on the Execution of his Office, he shall take the following Oath or Affirmation:--"I do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States, and will to the best of my Ability, preserve, protect and defend the Constitution of the United States."

Additionally, we note that the words required by the Constitution are described as an "Oath or Affirmation," and that the President is allowed to simply affirm his faithfulness to the Constitution. The word "affirmation" was inserted in this section precisely to allow Presidents to avoid swearing oaths to God as a condition of taking office. This provision seems particularly intended for Quakers (who had religious objections to taking oaths), but it is worded broadly enough to encompass any person who objects to taking an oath, including non-theists.

At the time of the Constitution several states allowed Quakers to escape taking an oath as a condition of assuming elected office. The 1780 Constitution of the state of Massachusetts, for example, provided that:

when any person shall be of the denomination called Quakers, and shall decline taking said oath, he shall make his affirmation in the foregoing form, omitting the words "swear" and inserting, instead thereof, the word "affirm," and omitting the words "So help me God," and subjoining, instead thereof, the words, "This I do under the pains and penalties of perjury."

Nothing in this section requires that the oath of office be taken on the Bible. Neither do the words "so help me God" appear in the oath. While Presidents often include this phrase in their inauguration ceremonies, the words are customary; they are not required by the Constitution and have no legal significance.

Oaths of office for other federal and state officials are described in Article VI of the Constitution:

The Senators and Representatives before mentioned, and the Members of the several State Legislatures, and all executive and judicial Officers, both of the United States and of the several States, shall be bound by Oath or Affirmation, to support this Constitution; but no religious Test shall ever be required as a Qualification to any Office or public Trust under the United States.

Joseph Story, an early Justice of the Supreme Court and the author of the first detailed commentary on the United States Constitution, comments on the oath or affirmation clause of the Constitution as follows:

Oaths have a solemn obligation upon the minds of all reflecting men, and especially upon those who feel a deep sense of accountability to a Supreme being. If, in the ordinary administration of justice in cases of private rights, or personal claims, oaths are required of those, who try, as well as of those, who give testimony, to guard against malice, falsehood, and evasion, surely like guards ought to be to be interposed in the administration of high public trusts, and especially in such, as may concern the welfare and safety of the whole community. But there are know denominations of men, who are conscientiously scrupulous of taking oaths (among which is that pure and distinguished sect of Christians, commonly called Friends, or Quakers,) and therefore, to prevent any unjustifiable exclusion from office, the constitution has permitted a solemn affirmation to be made instead of an oath, and as its equivalent (Joseph Story, Commentaries on the Constitution, 1833, pp. 1838ff.).

It's just a ritual from a more theocratic past, it doesn't really mean anything. My faith is people's testimony is in their legal accountability should they lie.

Swearing on the Bible is a LEGAL procedure. There are consequences to worry about in this world (not just the next), in this court (not just Judgment Day)- it doesn't really have much to do with theology. If people lie under oath they can be prosecuted, atheist or believer.

Athiest's are no longer required to swear on anything except for I think a personal type of declaration that they will tell the truth, as seen on TV SERIALS. But they once used the Bible because it invoked the fear of God. People who are afraid of God fear lying because they suppose their eternal souls to be in danger. But people with no FIXED moral compass can't really be trusted as much because they have no pre-supposed moral values that they think are as important as comapred to someone fearing the loss of their soul.