There are several theories as to why Judas betrayed Jesus. The most widely accepted one is this: Like most Israelites, Judas was expecting the Messiah to come in power as an earthly king. At that time, they hoped that he would come and overthrow the Romans and regain control of their land, and set up his earthly kingdom over them. (Kind of like a super King David). I believe that some of the other disciples may have had this hope as well - arguing over who would be the greatest in his kingdom? That sounds to me like maybe they thought that if Jesus did come and take control, he would appoint them in positions of honour. Unfortunately (for them) Jesus didn't come for that. A lot of scholars believe that Judas may have become disillusioned when Jesus began talking about his death. As for why Judas went to the priests, some say that it was because he'd lost faith in Jesus and wanted him out, or because he was trying to force Jesus' hand and make him use his power. Perhaps he hoped that when the mob came out to arrest Jesus, the Messiah would call upon his power to save himself. Either way it did not work, and Judas knew it. Afterwards, he knew he had condemned an innocent man. He went back to the Priests, but they laughed at him and told him it was his problem. He gave back the money they had paid him, then went out and hanged himself. It is a tragic story. There is nowhere in the bible that actually says why Judas betrayed him. This is basically a best guess by theologians and scholars.

Greed

According to the recently translated Judas Gospel, it was in fact under Jesus' direction that Judas was to betray him. He told Judas to do it. I'm currently reading The Lost Gospel, by Herbert Krosney . It delves into the gospel of Judas with partial translations from the surviving text. Interesting reading and exposes some of the Christian faith's attempts at covering up and expunging the gospel from within a few hundred years of the crucifixion.

He thought he could 'force' Jesus to face off with Rome. He never imagined that the Lord of Creation would allow Himself to be killed like that!

Today many speculate on the fate of Judas. But there is no need to do so in view of the Bible’s explicit testimony, even as the following will show. WHEN a baby boy was born to Mr. and Mrs. Simon Iscariot of the Judean village of Kerioth at the beginning of our common era, they had great hopes for him. As God-fearing parents they named him Judas, meaning “Praised,” it being the Greek form of Judah. But so far did Judas come short of their expectations that ever since no parents who are familiar with his life would think of naming a son Judas. Still Judas has many who make excuses for him. Typical of the opinion held by many professed Christians is that found in the Interpreter’s Bible. At John 18:2 it speaks of “The Mystery of Judas” and goes on to say that “at this point the Fourth Gospel grows . . . unsatisfying, particularly with regard to Judas. . . . Is there not a half hope for him in the man’s unbearable horror of himself and his deed?” “The love of Christ is very wonderful. And my experience of it makes me still harbor hopes for Judas—and for me.”—Vol. 8, pp. 754-757. True, mercy is a virtue we all must have and show if we would receive mercy. (Matt. 5:7) But in view of Jesus’ terming Judas “the son of destruction,” and saying of him: “It would have been finer for him if that man had not been born,” may we make excuses for Judas? No, we may not, even though needing mercy ourselves. Jesus, who understood the hearts of men better than any other man ever on earth, settles the matter for all who believe in the inspiration of the Bible. A careful consideration of its testimony will reveal that Judas poses no mystery whatever.—John 17:12; Matt. 26:24. It is of interest that Judas Iscariot seems to have been the only one of the twelve apostles who was not a Galilean, he being a Judean. In his day Palestine consisted of Judea, Galilee and Samaria. The Judeans looked down upon the Galileans, and both looked down even more upon the Samaritans. Also, the Galileans had a rather uncultured dialect or accent. That is why some doubted Peter’s denials of Jesus, his accent betraying him as a Galilean. It is very likely, therefore, that Judas considered himself better than the rest. His being made treasurer may also imply that he had a better education than the rest.—Matt. 26:73; Luke 22:59. However, while such facts may throw light on Judas’ disposition, they do not excuse his becoming a traitor. The Gospel writers certainly make no excuses for him. Matthew and Mark, in listing the twelve, not only place Judas last but add, “who later betrayed him”; while Luke makes it still stronger, “who turned traitor.” In fact, their righteous indignation is apparent in practically every reference they make to him.—Matt. 10:4; Mark 3:19; Luke 6:16. JUDAS GRADUALLY WENT BAD Nor did Jesus make any excuses for Judas. Aside from the foregoing, the only other references to Judas in the Gospel accounts, until the final week of Jesus’ earthly ministry, are Jesus’ strong words of condemnation of Judas, as recorded at John 6:64, 70. “Initially Jesus knew who were the ones not believing and who was the one that would betray him.” Not that Jesus deliberately chose a traitor, that is wholly unthinkable, but rather that as soon as Judas’ heart began going bad Jesus noticed it. In the same connection Jesus further said: “I chose you twelve, did I not? Yet one of you is a slanderer.” No doubt Judas got the force of those words even if the rest failed to do so. Incidentally, the word rendered “slanderer” is diabolos, a word that with but few exceptions is translated “Devil.” Obviously, Judas, day in and day out, was living a lie. At the beginning of his call he rejoiced in the good news of the Kingdom that Jesus preached. And like the others, he looked for an earthly kingdom. But in his case, in the struggle between love of righteousness and love of selfish gain, the love of selfish gain won out. Finding that the following of Jesus was a narrow and cramped path of self-denial, Judas began to cheat. He refused to pay the price but rewarded himself out of the common fund with which he was entrusted, for which reason John bluntly terms him a thief. Jesus’ warnings against greed and love of money fell upon deaf ears as far as Judas was concerned. Nor did he see anything inconsistent about his appropriating money from the common fund that had been contributed in appreciation for spiritual and physical healing received, while at the same time Jesus his Master had “nowhere to lay down his head.” In this Judas may be likened to Gehazi, the servant of Elisha, who sought to profit from his master’s healing of Naaman and who was stricken with leprosy. Judas’ selfishness caused him to be stricken with incurable spiritual leprosy, willful sin.—Matt. 8:20; 2 Ki. 5:1-27; Heb. 10:26-29. But “there is nothing hidden that will not become manifest, neither anything carefully concealed that will never become known.” And so circumstances finally did make plain to all that although Judas was associated with Jesus and his apostles, he was at heart not one of them. It was passovertime, A.D. 33, and “the chief priests and the Pharisees had given orders that if anyone got to know where he was he should give the information, in order that they might get their hands on him.” (Luke 8:17; John 11:57) Jesus and his disciples were guests at the home of Simon the leper when Mary, the sister of Lazarus and Martha, came and “took a pound of perfumed oil, genuine nard, very costly, and she poured it on the feet of Jesus and wiped his feet dry with her hair.” From Matthew’s and Mark’s accounts it appears that she also poured this perfumed oil upon Jesus’ head.—John 12:1-3. But this was too much for greedy, dishonest and unloving Judas. As the account goes on to say: “But Judas Iscariot, one of his disciples, who was about to betray him, said: ‘Why was it this perfumed oil was not sold for three hundred denarii and given to poor people?’ He said this, though, not because he was concerned about the poor, but because he was a thief and had the money-box and used to carry off the monies put in it. Therefore Jesus said: ‘Let her alone, that she may keep this observance in view of the day of my burial. For you have the poor always with you, but me you will not have always.’”—John 12:4-8. While both Matthew and Mark implicate others in this objection, from John’s account it appears that these merely joined Judas in what they thought was a reasonable point, not suspecting any ulterior motive. The sting of this rebuke for making an ostensibly reasonable objection, as noted by others siding in with him, caused Judas to allow bitterness, hate and the Devil himself to enter his heart. “Then,” as Matthew tells us, “Judas Iscariot . . . went to the chief priests and said: ‘What will you give me to betray him to you?’ They stipulated to him thirty silver pieces. So from then on he kept seeking a good opportunity to betray him.”—Matt. 26:14-16; Mark 14:3-11. The role that greed played in Judas’ course will be better appreciated when we note just what was involved in the way of values. True, the thirty silver pieces or shekels, the price of a slave, may have come to as little as $12.00. (Ex. 21:32) And the 300 denarii is valued at $51.00. But in Jesus’ day a denarius, according to Clarke’s Commentary, was an average day’s wages. At that rate the sum Judas received amounted to two and a half months’ wages, while the costly perfumed oil represented a whole year’s pay, considering they did not work on sabbath or feast days.—Matt. 20:2. Further indicating the depth of Judas’ depravity is his being able to meet with the twelve to celebrate the annual passover, hypocritically feigning to enter into the spirit of the occasion as did the rest. Note also his temerity on that evening to ask, after Jesus had announced that one of them would betray him: “It is not I, is it, Rabbi?” Jesus’ reply, “That was for you to say,” may have sounded cryptic to the rest, but without a doubt Judas got the full import of it, even as Judas also did of Jesus’ further remarks to him, “What you are doing get done more quickly.”—Matt. 26:25; John 13:21-30. Having dismissed Judas as one unworthy to be present, Jesus then instituted the memorial of his death, “the Lord’s evening meal,” or “the Lord’s supper,” as it is more commonly called. After that meal and Jesus’ farewell counsel to them he and the eleven went out into the garden of Gethsemane, where Jesus prayed. Shortly thereafter, Judas “came and with him a great crowd with swords and clubs from the chief priests and older men of influence of the people. And going straight up to Jesus he said: ‘Good day, Rabbi!’ and kissed him very tenderly. But Jesus said to him: ‘Fellow, for what purpose are you present?’” “Judas, do you betray the Son of man with a kiss?”—Matt. 26:47, 49, 50; Luke 22:48. NOT DESERVING OF PITY A murderer may kill in cold blood and then, seeing the results of his crime, feel remorse. It was that way with Judas. His deed was not one done on the spur of the moment due to pressure and fleshly weakness, as was the case with Peter’s denial of his Master three times. No, with Judas there was involved malice, pride, hypocrisy, scheming and sticking to a predetermined course. It is also necessary to bear in mind that because of his bad heart condition Satan was able to enter and spur him on. That he afterward felt remorse because of the burden of guilt or of its penalty does not excuse him. Like Esau, he shed tears in vain. He himself realized that fact, and being unable to live with himself any longer he committed suicide, admitting moral bankruptcy. So we read: “Then Judas, who betrayed him, seeing he had been condemned, felt remorse and turned the thirty silver pieces back.” The priests refusing the money, Judas then “threw the silver pieces into the temple and withdrew, and went off and hanged himself.”—Matt. 27:3-10. In passing let it be noted that while Bible critics make much of the fact that Matthew’s account given above differs from what Peter said about Judas “pitching head foremost he noisily burst in his midst and all his intestines were poured out,” they do not contradict each other. It has been suggested that Judas hanged himself from a tree on a craggy terrain. The rope or branch breaking, Judas’ end could be just as described by Peter.—Acts 1:16-18. Thus the facts as recorded in the Scriptures help us to understand why Jesus referred to Judas as “the son of destruction” and why he said of him that “it would have been finer for him if that man had not been born.” There is no justification for theorizing about “the mystery of Judas”; and to try to make excuses for him will lead us into the twofold snare of rebellion and carelessness. Since God’s judgment makes Judas’ case hopeless, it is rebellion on our part to extend him sympathy. This rule God repeatedly stated in his dealings with his people Israel. Thus when Nadab and Abihu were struck dead by Jehovah for offering illegitimate fire, Jehovah warned that Aaron and his remaining sons should not mourn for them. When Samuel mourned over Saul’s rejection as king, God rebuked him for it. And repeatedly we read of Jeremiah’s being told regarding his willfully wicked people: “Pray not thou for this people, neither lift up cry nor prayer for them, neither make intercession to me; for I will not hear thee.” Our attitude at all times must be as expressed: “Great and wonderful are your works, Jehovah God, the Almighty. Righteous and true are your ways, King of eternity.”—Jer. 7:16, AS; Rev. 15:3. And for us to hold out hope for Judas would encourage us to become careless. If there is hope for the archtraitor, the betrayer of the Son of God, there will also be hope for us regardless of what we may do, since we simply could not descend that low, God’s Son nevermore coming to earth as a man. But no, we must realize that Judas must have started out right or Jesus would not have chosen him. But he permitted selfishness to get the upper hand and eventually surrendered to the Devil. His end therefore forcibly drives home to us the counsel found at Proverbs 4:23: “More than all else that is to be guarded, safeguard your heart, for out of it are the sources of life.”

There's an article written by Thomas H. Maugh II, from the Los Angeles Times, and re-printed on the Clevealnd's local newspaper-The Plain Dealer-in 2006. The written article is about a document, called "The Gospel Of Judas", considered to be the most important archaeological finding of the last sixty years, in which--according to the document--no such a thing as "betrayal" of Jesus by Judas ever took place. Not only that, in addition, "no mention is made of the crucifixion or the so-called resurrection". The document, a book rejected by early church, says Jesus [arranged] his own betrayal. It also says that Judas Iscariot, long reviled as history's quintessential "betrayer", was actually the best friend of Jesus, and "turned him over to authorities at Jesus's own request". Most copies were destroyed. The sole known copy lay hidden in the Egyptian desert for nearly 1,700 years before it was discovered by looters in the 1970s.

Because someone had to. Jesus had said that one of his apostles would and God cannot be wrong. In order for Jesus's destiny to be fulfilled, one of them had to betray him. Judas drew the spiritual short straw. That's my interpretation of it.

Apparently, Judas was a Sicarri, which was a more extreme version of a Zealot. He tried to push Jesus into acting in power by turning him over to the Sanhedrin. When they turned Jesus over to the Romans, Judas felt betrayed, and so did the one thing he believed would get him some measure of revenge. He hanged himself in front of the Annas family tomb, in order to desecrate it, and make eternal rest for that family impossible.