This is the Book (the Qur-an), whereof there is no doubt, a guidance to those who are Al-Muttaqun [the pious and righteous persons who fear Allah much (abstain from all kinds of sins and evil deeds which He has forbidden) and love Allah much (perform all kinds of good deeds which He has ordained)].  Surah (Chapter) al-Baqarah (The Cow) Qur-an 2:2

The Qur-an is the final version of the same Message that Allah (God) had sent earlier to mankind through many of His Rusul (Messengers).
The Holy Qur-an is the source of all Islamic religious beliefs and practices. It is the most read and the most quoted book in the world. This is the only Book, which has been memorized by millions of people by heart since its revelation. 
The Qur-an was revealed in small portions over a period of 23 years. There are 114 Chapters in the Qur-an. Each chapter of Qur-an is called a Surah. Each Surah (Chapter) is divided into various Ayat (Verses). Some Suwar (Chapters-Plural of Surah) contain more verses while others less. Surah al-Baqarah, the second chapter of the Qur-an, is the biggest of all. It contains 286 Ayat (Verses). The shortest Surah of the Qur-an is Surah al-Kauthar (A river in Paradise). It contains only three Ayat (Verses). Though there are other Suwar (Chapters-Plural of Surah) that contain only three Ayat (Verses) but they contain more words and lengthy sentences. The other Suwar (Chapters-Plural of Surah) which contain only three Ayat (Verses) are Surah al-‘Asr (The Time) and Surah an-Nasr (The Help).
(Suwar is the plural of Surah and Ayat is the plural of Ayah).

The Qur-an is also divided into thirty almost equal portions. Each of these portions is called a Juz in Arabic.

The Qur-an was revealed to the Messenger of Allah, Muhammad S in small portions. Some portions of the Qur-an were revealed in Makkah while other portions of it were revealed in Madinah. The Suwar (Chapters-Plural of Surah) that were revealed in Makkah, are known as Makki Suwar. The Suwar (Chapters-Plural of Surah) revealed in Madinah after Hijrah (Migration), are known as Madani Suwar.  

The Makkan period of revelation was from 610 AD to 622 AD. The Madani period was from 622 AD to 632 AD. Eighty-six (86) Suwar (Chapters-Plural of Surah) were revealed in Makkah, and twenty-eight (28) Suwar (Chapters-Plural of Surah) were revealed in Madinah.

Makki Suwar (Chapters-Plural of Surah) contain 4417 Ayat (Verses), Madani Suwar (Chapters-Plural of Surah) contain 1819 Ayat (Verses).
The total number of Ayat (Verses) in the Hoy Qur-an is six thousand two hundred thirty six (6,236).

The Messenger of Allah, Muhammad S received the first Wahi (Message from Allah) in 610 AD, in the small cave in the mountain of Hira. That mountain is now known as Jabl Nur (Mountain of Radiance). It is located about two and a half miles (Four Kilometers) away from the Ka’bah in the city of Makkah.

In the first Wahi (Message from Allah), the Messenger of Allah, Muhammad S received the first five Ayat (Verses) of Surah (Chapter) al-‘Alaq (The Clot).

Iqra bismi rabbik-allazi khalaq. Read in the name of your Lord who created,

Khalaqal insana min ‘alaq. created man from a clot.

‘Iqra’ wa rabbukal akram. Read, for your Lord is most Generous,

Allazi 'allama bil qalam. Who teaches by means of the pen,

'Allamal insana ma lam ya’lam. teaches man what he does not know. Surah (Chapter) al-’Alaq (The Clot) Qur-an 96:1-5

The last revelation of the Qur-an was the two hundred eighty-first Ayah (Verse) of Surah (Chapter) Al-Baqarah (The Cow).

And be afraid of the Day when you shall be brought back to Allah. Then every person shall be paid what he earned, and they shall not be dealt with unjustly. Surah (Chapter) al-Baqarah (The Cow) Qur-an 2:281

Surah al-Fatihah (The Opening Chapter) was the first complete chapter to be revealed and Surah an-Nasr was the last.

When the Qur-an was being revealed, the Messenger of Allah, Muhammad S used to recite the revealed verses to his Sahabah (Companions). They used to learn these verses by heart. Some of the companions used to write them on palm leaves, animal hides and stone tablets etc. The Suwar (Chapters) and Ayat (Verses) of the Qur-an are not arranged in their chronological order of revelation. The Messenger of Allah, Muhammad S used to set the place of various Suwar (Chapters) and Ayat (Verses) himself.

There were several designated Katib Al-Wahi (Writer of Messages from Allah) who used to write down the divine revelations whenever the Messenger of Allah, Muhammad S received them.

After the demise of the Messenger of Allah, Muhammad S, many newly converted tribes revolted. Most of them decided to follow most principles of Islam, except the institution of Zakah (Poor Due Charity). One cannot pick and choose beliefs in Islam. There is no compromise with the basic Islamic beliefs.
Abu Bakr R, a prominent Sahabi (Companion of Muhammad S) became the first Khalifah (Caliph) of Muslims. Soon after assuming this responsibility, he had to face severe challenges in the form of several revolts. He also had to face challenges from several claims of false Prophethood from several apostates. He decided to firmly deal with them. He sent Muslim armies to suppress the rebellion. As a result, many of those Huffaz (Those who had memorized Qur-an by heart) died.
‘Umar bin Khattab R, another prominent Sahabi (Companion of Muhammad S) pondered upon the situation. He felt an urgent need to compile the scattered portions of the Qur-an into one volume. He suggested it to Abu Bakr R, who was initially reluctant to undertake such a task. His reasoning was that since the Messenger of Allah, Muhammad S did not make any such compilation during his lifetime, so how could he? But after thinking over the matter, he agreed to ‘Umar bin Khattab R’s suggestion. Subsequently, a committee was set up for compiling the Qur-an. It was headed by Zayd bin Thabit R, the secretary of the Messenger of Allah, Muhammad S, who also was the main Katib Wahi (Writer of Messages from Allah). This team compiled the Holy Qur-an in one volume. This copy of the Qur-an was verified by all Sahabah (Companions of Muhammad S) who used to memorize each Ayah (Verse) and Surah (Chapter) of the Qur-an as it was revealed to the Messenger of Allah, Muhammad S.

This copy of the Qur-an was kept in the custody of Hafsah bint ‘Umar R, a widow of the Messenger of Allah, Muhammad S. After Abu Bakr R, ‘Umar bin Khattab R became the second Khalifah (Caliph) of Muslims, but he, for some reason, did not publish the compiled version of the Qur-an.
It was during the tenure of the third Khalifah (Caliph) of Muslims, ‘Uthman bin ‘Affan R, a standardized version of the Qur-an was made from the available document and its copies were sent to all other towns and cities. The Qur-an which we read today is the exact copy of the one published by the third Khalifah (Caliph) of Muslims, ‘Uthman bin ‘Affan R.  

There are three main themes of theQur-an, Wahdah (Oneness of Allah), Risalah (Allah‘s Messengers and the finality of the Messengers) and Akhirah (Day of Judgment and life after death).

The main emphasis of the Qur-an is Tawhid i.e. the Oneness of God, and the finality of the Messengership of Allah, Muhammad S. Besides, it contains the stories of previous Messengers, moral teachings and the injunctions of Shari’ah. It also informs us about other revealed books, about angels, about the Last Day of Judgment and Paradise and Hell.

The Qur-an is the most comprehensive book of law. It deals with each and every aspect of human life. Its rules are easy and simple. It does not unnecessarily stress mankind. It does not lead to asceticism. It clearly states:

“God desires ease for you while you desire hardship.” (2:185)

S: Sallallahu 'Alayhi Wasallam
R: Radiallahu Anhu