Islam is the largest religion of Bangladesh, the Muslim population is over 130 million (the Fourth-largest Muslim population in the world after Indonesia, India and Pakistan), and constitute nearly 88% of the total population, based on the 2001 Census. Religion has always been a strong part of identity, but this has varied at different times. A survey in late 2003 confirmed that religion is the first choice by a citizen for self-identification; atheism is extremely rare. Islam is the official religion of The People's Republic, as stated in the Constitution of Article 2A (inserted by the Constitution Eighth Amendment Act, 1988). The United Nations has recognised the country as mainly moderate Muslim democratic country, but however in recent years there has been an increase in Islamism among some political parties.
The majority of Muslims in Bangladesh are Sunni (Deobandi), who mainly follow the Hanafi school of teachings, many follow the barelwi movement, and there are also large numbers of Sufis. There are also few people who are Ahmadiyya and Shi'a Muslims - most of those who are Shi'a reside in urban areas. The Shi'a observance commemorating the martyrdom of Ali's sons, Hasan and Husayn, are still widely observed by the nation's Sunnis, even though there are small numbers of Shi'as. The Ahmadiyya Muslim Community, which is claimed to be non-Muslim by mainstream Muslim leaders, is estimated to be around 100,000, the community has faced discrimination because of their belief and have been persecuted in some areas.
Islam arrived to the region of Bengal since the 13th century, mainly by the arrivals of Arab traders, Persian Saints and conquests of the region. One of the notable Muslim saint was, Shah Jalal. He arrived in the region of Sylhet in 1303 with many other disciples to preach the religion to the people.
During the opening years of the 13th century, the Muslim conquest of Bengal took place, mainly as a sequel to Muhammad Ghori's expeditions late in 1192 spanning northern India. Syed Shanasiruddin was originally from Iraq but came to Bangladesh to spread the Islam. Early Arab Muslims however established commercial as well as religious contacts within the region before the conquest, mainly through the coastal regions as traders and primarily via the ports of Chittagong. Arab navigation in the region, was the result of the Muslim reign over the Indus delta. The activities of the Muslims were expanded along the entire coast of South Asia including the coasts of Bengal. The religion of Islam entered the region in many different ways, the Muslim traders, the Turkish conquest and, the missionary activities of the Muslim Sufis. One of the authentications of the Arab traders present in the region was, the writings of Arab geographers, found in the mouth if the Meghna River located near Sandwip, on the Bay of Bengal. This evidence suggests that the Arab traders had arrived along the Bengal coast long before the Turkish conquest. The Arab writers also knew about the kingdoms of Samrup and Ruhmi, the latter being identified with the empire of Dharmapal of the Pala Empire.
Muslim saints began to teach the Islamic principles of equality while the rulers took steps to build up Muslim culture on the basis of a casteless society. Many Buddhists and Hindus chose to identify themselves with the Muslims in order to be free from social injustice and to gain equality and good position in society. As a result of large-scale conversion, many local beliefs, not allowed by the Islamic dogma but useful in achieving compromise, found their ways into the Muslim society of Bengal.
Between the 8th century and 12th century, the Buddhist dynasty known as the Pala Empire ruled Bengal. During that time, the majority of the population in Bengal were thought to be Buddhists. After the decline of the Pala dynasty, the Sena dynasty came to power. Sena rulers were Hindu dynasty that imposed Hinduism and the caste system rigidly. When the Muslim rulers came, many Buddhists and lower caste Hindus welcomed them and accepted Islam, and others became Muslims for the purpose of fitting in into society with other Muslims. The large scale conversion to Islam of the population of what was to become Bangladesh began in the thirteenth century and continued for hundreds of years. Conversion was generally collective rather than individual. Islam, attracted numerous Buddhists, and Hindus. Sufis were responsible for most conversions.
Before the conquest by the Muslims, Sylhet was ruled by local chieftains. In 1303 the saint, Hazrat Shah Jalal, came to Sylhet from Delhi with a band of 360 disciples to preach Islam and defeated the Raja Gour Gobinda. As a result, Sylhet developed into a region that was home to numerous saints and Islamic shrines His uncle, Sheikh Kabir, one day gave Shah Jalal a handful of earth and asked him to travel to Hindustan with the instruction that he should settle down at whichever place in Hindustan whose soil matched completely in smell and color, and devote his life for the propagation and establishment of Islam there. Shah Jalal journeyed eastward and reached India in 1300, where he met with many great scholars and mystics. He arrived at Ajmer, where he met the great Sufi mystic and scholar, Pir Khawaja Gharibnawaz Muinuddin Hasan Chisty, who is credited with much of the spread of Islam in India. In Delhi, he met with Nizamuddin Auliya, another major Sufi mystic and scholar.
During the later stages of his life, Shah Jalal devoted himself to propagating Islam to the masses. Under his guidance, many thousands of Hindus and Buddhists converted to Islam. Shah Jalal become so renowned that even the famed Ibn Battuta, whilst in Chittagong, was asked to change his plans and go to Sylhet to visit him. On his way to Sylhet, Ibn Batuta was greeted by several of Shah Jalal's disciples who had come to assist him on his journey many days before he had arrived. Once in the presence of Shah Jalal, Ibn Batuta noted that Shah Jalal was tall and lean, fair in complexion and lived by the masjed in a cave, where his only item of value was a goat from which he extracted milk, butter, and yogurt. He observed that the companions of the sheikh were foreign and known for their strength and bravery. He also mentions that many people would visit the sheikh and seek guidance. Shah Jalal was therefore instrumental in the spread of Islam throughout north east India including Assam.
The tradition of Islamic mysticism known as Sufism appeared very early in Islam and became essentially a popular movement emphasizing worship out of a love of God rather than fear. Sufism stresses a direct, unstructured, personal devotion to God in place of the ritualistic, outward observance of the faith and "a Sufi aims to attain spiritual union with God through love" An important belief in the Sufi tradition is that the average believer may use spiritual guides in his pursuit of the truth. Throughout the centuries many gifted scholars and numerous poets have been inspired by Sufi ideas.
Sufi masters were the single most important factor in South Asian conversions to Islam, particularly in Bangladesh. Most Bangladeshi Muslims are influenced by Sufism. However, there are many movements who were against Sufism and are still active in Bangladesh today. These include the Deobandi(sunni) and Wahabi(sunni) or Salafi(sunni) movements.
The Qadiri, Naqshbandi, Chishti, Mojaddidi, Ahmadi, Mohammadi, Sohradi and Refai orders were among the most widespread Sufi orders in Bangladesh in the late 1980s. The beliefs and practices of the first two are quite close to those of orthodox Islam; the third, founded in Ajmer, India, is peculiar to religion in the subcontinent and has a number of unorthodox practices, such as the use of music in its liturgy. Its ranks have included many musicians and poets.
Although a formal organization of ordained priests has no basis in Islam, a variety of functionaries perform many of the duties conventionally associated with a clergy and serve, in effect, as priests. One group, known collectively as the Ulama, has traditionally provided the orthodox leadership of the community. The Ulama unofficially interpret and administer religious law. Their authority rests on their knowledge of Sharia, the corpus of Islamic jurisprudence that grew up in the centuries following the Prophet's death.
The members of the Ulama include Maulvis, Imams, and Mullahs. The first two titles are accorded to those who have received special training in Islamic theology and law. A maulvi has pursued higher studies in a madrassa, a school of religious education attached to a mosque. Additional study on the graduate level leads to the title maulana. The madrassas are also ideologically divided in two mainstreams. The Ali'a Madrassa which has its roots in Aligarh movement of Sir Syed Ahmed Khan Bahadur and the other one is Quomi Madarassa which is very close to Deobandi schools in India and Pakistan founded by Haji Muhammad Abid of Deoband, India. This means the Ulamas are also not in full agreement about their interpretation of Islam, of its theology and law.
In Bangladesh, where a modified Anglo-Indian civil and criminal legal system operates, there are no official sharia courts. Most Muslim marriages, however, are presided over by the qazi, a traditional Muslim judge whose advice is also sought on matters of personal law, such as inheritance, divorce, and the administration of religious endowments.
In the late 1980s, the ulama of Bangladesh still perceived their function as that of teaching and preserving the Islamic way of life in the face of outside challenges, especially from modern sociopolitical ideas based on Christianity or communism. Any effort at modernization was perceived as a threat to core religious values and institutions; therefore, the ulama as a class was opposed to any compromise in matters of sharia. Many members of the ulama favored the establishment of an Islamic theocracy in Bangladesh and were deeply involved in political activism through several political parties.
Source: Amardesh 
The Constitution establishes Islam as the state religion but provides for the right to practice—subject to law, public order, and morality—the religion of one's choice. The Government generally respects this provision in practice; however, some members of the Hindu, Christian, Buddhist, and Ahmadiya communities experience discrimination. The Government (2001–2006) led by an alliance of four parties Bangladesh Nationalist Party, Jamaat-e-Islami Bangladesh, Islami Oikya Jote and Bangladesh Jatiyo Party banned the Ahmadiya literatures by an executive order.
Family laws concerning marriage, divorce, and adoption differ depending on the religion of the person involved. There is also, Anglo-Indian Civil Law in some of these regards in parallel. There are no legal restrictions on marriage between members of different faiths but to get marriage registered under Muslim religious laws, the bride and the bride-groom must be Muslims by birth or by conversion.
Under the Muslim Family Ordinance, female heirs inherit usually half of that inherited by male relatives, and wives have fewer divorce rights than husbands. Men are permitted to have up to four wives, although society strongly discourages polygamy, and it is practiced rarely. Laws provide some protection for women against arbitrary divorce and the taking of additional wives by husbands without the first wife's consent, but the protections generally apply only to registered marriages. Marriage is governed by family law of the respective religions. In rural areas, marriages sometimes are not registered because of ignorance of the law. Under the law, a Muslim husband is required to pay his former wife a lump sum alimony fixed at the time of registraton of marriage and further variable amount of alimony for 3 months for maintenance, but this law is not always enforced in the rural areas.
Post-1971 regimes sought to increase the role of the government in the religious life of the people. The Ministry of Religious Affairs provided support, financial assistance, and endowments to religious institutions, including mosques and community prayer grounds (idgahs). The organization of annual pilgrimages to Mecca also came under the auspices of the ministry because of limits on the number of pilgrims admitted by the government of Saudi Arabia and the restrictive foreign exchange regulations of the government of Bangladesh. The ministry also directed the policy and the program of the Islamic Foundation Bangladesh, which was responsible for organizing and supporting research and publications on Islamic subjects. The foundation also maintained the Baitul Mukarram (National Mosque), and organized the training of imams. Some 18,000 imams were scheduled for training once the government completed establishment of a national network of Islamic cultural centers and mosque libraries. Under the patronage of the Islamic Foundation, an encyclopedia of Islam in the Bangla language was being compiled in the late 1980s.
Another step toward further government involvement in religious life was taken in 1984 when the semiofficial Zakat Fund Committee was established under the chairmanship of the president of Bangladesh. The committee solicited annual zakat contributions on a voluntary basis. The revenue so generated was to be spent on orphanages, schools, children's hospitals, and other charitable institutions and projects. Commercial banks and other financial institutions were encouraged to contribute to the fund. Through these measures the government sought closer ties with religious establishments within the country and with Islamic countries such as Saudi Arabia and Pakistan.
Islam being the central component of national identity plays a significant role in the politics, life and culture of the people. Secular parties such as Awami League also mention "Allah is Great" as a slogan in their banners. When in June 1988 an "Islamic way of life" was proclaimed for Bangladesh by constitutional amendment, very little attention was paid outside the intellectual class to the meaning and impact of such an important national commitment. Most observers believed that the declaration of Islam as the state religion might have a significant impact on national life, however. Aside from arousing the suspicion of the non-Islamic minorities, it could accelerate the proliferation of religious parties at both the national and the local levels, thereby exacerbating tension and conflict between secular and religious politicians. Unrest of this nature was reported on some college campuses soon after the amendment was promulgated.
Jamaat-e-Islami Bangladesh (a.k.a 'Jamaat') is the largest Islamist political party in Bangladesh. This is one of the leading political party in Bangladesh and largest islamic party in subcontinent. The party joined the Bangladesh Nationalist Party to lead government and hold two key Ministries with Khaleda Zia's government. This party played a questionable role in Liberation War of Bangladesh. It is alleged that the current leader of the party, Motiur Rahman Nizami (as well as previous leaders, and other party members) participated in alongside the Pakistani army in perpetrating the 1971 Bangladesh atrocities as Razakars and members of the Al-Badr militias.