This is a question that can not be answered with complete accuracy in a few words. The split began with a dispute over who should rightfully have been named the successor to Mohammad's leadership of the Islamic faithful. (This split took place much later than the events in question and took place over many years.) The Shia believe the rightful successor was Ali and should have continued through the family line of Mohammad. The Sunni believe Abu Bakr and his successors were the rightful leadership. Since then, differences in methodologies and interpretations regarding the extraction of law from the Quran and the Sunna have multiplied. Other differences lie in attitudes toward government, belief in a messianic figure, certain holy days, beliefs about the infallibility of the Imams, particular details about the nature of God, etc. They do have the basics in common, and most adherents to either group would not call the others heretics (though there are some on both sides who consider the other side to be outside of the faith). For a more detailed (but still concise) answer to this question, go to http://en.wikipedia.org/wiki/Shi'a_Islam#Shi.26.23x02bb.3Ba_Contrasted_with_Sunni and click on "Shi'a contrasted with Sunni" and good luck!

The last paragraph probably best answers your question, but all of it applies to their differences. Both Sunni and Shia Muslims share the most fundamental Islamic beliefs and articles of faith. The differences between these two main sub-groups within Islam initially stemmed not from spiritual differences, but political ones. Over the centuries, however, these political differences have spawned a number of varying practices and positions which have come to carry a spiritual significance. The division between Shia and Sunni dates back to the death of the Prophet Muhammad, and the question of who was to take over the leadership of the Muslim nation. Sunni Muslims agree with the position taken by many of the Prophet's companions, that the new leader should be elected from among those capable of the job. This is what was done, and the Prophet Muhammad's close friend and advisor, Abu Bakr, became the first Caliph of the Islamic nation. The word "Sunni" in Arabic comes from a word meaning "one who follows the traditions of the Prophet." On the other hand, some Muslims share the belief that leadership should have stayed within the Prophet's own family, among those specifically appointed by him, or among Imams appointed by God Himself. The Shia Muslims believe that following the Prophet Muhammad's death, leadership should have passed directly to his cousin/son-in-law, Ali. Throughout history, Shia Muslims have not recognized the authority of elected Muslim leaders, choosing instead to follow a line of Imams which they believe have been appointed by the Prophet Muhammad or God Himself. The word "Shia" in Arabic means a group or supportive party of people. The commonly-known term is shortened from the historical "Shia-t-Ali," or "the Party of Ali." They are also known as followers of "Ahl-al-Bayt" or "People of the Household" (of the Prophet). From this initial question of political leadership, some aspects of spiritual life have been affected and now differ between the two groups of Muslims. Shia Muslims believe that the Imam is sinless by nature, and that his authority is infallible as it comes directly from God. Therefore, Shia Muslims often venerate the Imams as saints and perform pilgrimages to their tombs and shrines in the hopes of divine intercession. Sunni Muslims counter that there is no basis in Islam for a hereditary privileged class of spiritual leaders, and certainly no basis for the veneration or intercession of saints. Sunni Muslims contend that leadership of the community is not a birthright, but a trust that is earned and which may be given or taken away by the people themselves. Shia Muslims also feel animosity towards some of the companions of the Prophet Muhammad, based on their positions and actions during the early years of discord about leadership in the community. Many of these companions (Abu Bakr, Umar, Aisha, etc.) have narrated traditions about the Prophet's life and spiritual practice. Shia Muslims reject these traditions (hadith) and do not base any of their religious practices on the testimony of these individuals. This naturally gives rise to some differences in religious practice between the two groups. These differences touch all detailed aspects of religious life: prayer, fasting, pilgrimage, etc. Sunni Muslims make up the majority (85%) of Muslims all over the world. Significant populations of Shia Muslims can be found in Iran and Iraq, and large minority communities in Yemen, Bahrain, Syria, and Lebanon. It is important to remember that despite all of these differences in opinion and practice, Shia and Sunni Muslims share the main articles of Islamic belief and are considered by most to be brethren in faith. In fact, most Muslims do not distinguish themselves by claiming membership in any particular group, but prefer to call themselves simply, "Muslims." http://islam.about.com/cs/divisions/f/shia_sunni.htm

- Though I would like to tell you the difference between the two, I am going to avoid it because of the heated arguments it may cause from the 2 sects, so I will let someone else do that (sorry). I will answer the other part of your question: - I am JUST Muslim, neither Shia or Sunni (though my parents are Shia). Note: Shia & Sunni are not the only 2 sects in islam. there are more sects but Shia & Sunni are the 2 largest/major sects. You can be just Muslim (and in my opinion) it is the better option (as believing in Allah, Mohammed, all his prophets, the Day of Judgement & praying to god is the basics of what Islam is).

As the created the duty of all human beings is to obey the Creator, God. HQ 4:80 says "He who obeys the Messenger, has certainly obeyed God" Did the Messenger say we have to be Sunni or Shia? The answer is a definite NO. While HQ 33:21 says "Ye have indeed in the Messenger of God a beautiful pattern (of conduct to follow) for any one whose hope is in God and the Final Day, and who engages much in the Praise of God." So what about his example did he become Shia or Sunni? Again the answer is a definite NO. The NO is definite in both cases because there was no Sunni/Shia divide at any point during his lifetime. When one of his wives was asked about Prophet Mohammed's character she said his character was the Qur'an. That is he lived by it in every aspect of his life. And the advice the Prophet is reported to have left in his last sermon was 'I leave with you two things which if you hold fast onto you will never go astray - the Qur'an and my Sunnah (my way)"

Shia Muslims feel animosity towards some of the companions of the Prophet Muhammad, based on their positions and actions during the early years of discord about leadership in the community. Many of these companions (Abu Bakr, Umar, Aisha, etc.) have narrated traditions about the Prophet's life and spiritual practice. Shia Muslims reject these traditions (hadith) and do not base any of their religious practices on the testimony of these individuals. This naturally gives rise to some differences in religious practice between the two groups. These differences touch all detailed aspects of religious life: prayer, fasting, pilgrimage, etc. Sunni Muslims make up the majority (85%) of Muslims all over the world. Significant populations of Shia Muslims can be found in Iran and Iraq, and large minority communities in Yemen, Bahrain, Syria, and Lebanon. It is important to remember that despite all of these differences in opinion and practice, Shia and Sunni Muslims share the main articles of Islamic belief and are considered by most to be brethren in faith. In fact, most Muslims do not distinguish themselves by claiming membership in any particular group, but prefer to call themselves simply, "Muslims."

Apparently, Sunni Muslims believe that new leaders should be elected from among those capable of the job. Shiites, OTOH, believe that the leadership should follow Mohammed's blood line.

asalam o alikum brothers , i m sunni practising muslim and i totaly agree with the impresin i come up with after reading the post that difrences between shias and sunnis are more to do with political philosphy between the two sects other wise we are quite a same. our shia brothers have a specific idea of imamt and we sunnis consider and follow the shura concept, globaly thier are signs of shia sunni unification against the odds , most sunni youngsters like me really consider leaders like aaqa-e-khaminee and hassan nasrullah as the new horizon of fight against the imperialists forces and spreading the true essence of fredom and independence the more we collabarate more will prosper.

Basic difference is shias concept of Imamat , Muslims believe there is no one with devine guidance after Mohammad (Saw)evry one can be challenge on the basis of quran & hadith .None has an authority to be a last word . Thats why the person like abu Bakr(ra) said follow me in rights but straigthen me when i go wrong ,Omar (ra) took his decission, about mahar ,back when an old lady reffered to Quran. This is the methodology which Islam gives . But Shias believe there r 12 Imams who r devinly guided and infallible .They r authority in religion ,their words r the last words and unchallenge able .And imam has to interpret Quran & hadith their twelve imams guided them and 12th imam is still guiding . So shias source of Knowledge is their self made imams. Which holds no position in real Islm As Source of Knowledge is different ,so there are many differences is generated .