Bangla Script grew out of Kutila, which was a reformed version of Brahmi. Although the Brahmi script is believed to have evolved in the ancient past, its earliest specimens are two inscriptions, dating from the 5th century BC, discovered at Pipraba and Bali. From 350-100 BC the Brahmi script, now known as Ashoka or Maurya script, underwent certain transformations. Asoka script or Maurya script can be divided into two stages: ancient and modern. Ancient Maurya script had two forms: uttari and daksini. Modern script evolved through seven stages.

The second stage in the evolution of the Brahmi script is into the Kushan script, named after the Kushan royal dynasty and in use upto 100-300 AD. The third stage of its evolution was into the Gupta script, named after the Gupta royal dynasty, and current between the 4th and 5th centuries AD. During this period, some letters of the Gupta script took the shape of modern Bangla letters. For instance, in Maharaja Jayanatha's grant, B and M are similar to the Bangla letters today.

The next stage in the evolution of the Brahmi script was into the Kutila script, current between the 6th to 9th centuries. The name perhaps comes from the fact that Kutila letters and vowel symbols are rather complex (Kutila, meaning complicated). Almost all modern scripts of India have grown out of the two main forms of the Kutila script. Devanagari evolved from the west regional form of north-Indian Kutila, while Bangla evolved from its eastern or Magadha form. The transformation of eastern Kutila script began in the 6th century AD. Some time during the reign of the Gurjara kings, most possibly during the reign of Mahendrapala I, son of Bhoja, Kutila script entered Bengal. The copperplate inscriptions of his son Vinayakapala, dating from the 10th century AD, are in the Kutila script. Kutila script evolved further, finally developing into the basic Bangla script towards the end of the 10th century AD. Specimens of this writing are to be found in the Bangad grant of King Mahipala I (980-1036) and the Irdar grant of King Nayapaladeva (1036-1053). The Bangad grant shows the following fully developed modern Bangla letters: অ৴ উ৴ ক৴ খ৴ গ৴ চ৴ ঢ৴ ব৴ হ৴ ও,  and জ.

An improved form of Bangla script is seen in vijayasena's (1098-1160) Deopada inscription. By the end of the 12th century, the script had almost assumed its present form, as may be seen in laksmanasena's Anuliya grant and the Sundarban grant of 1196. The Muslim conquest of Bengal in 1204 AD briefly halted the development of bangla literatureand culture, as well as further evolution of the Bangla script. However, under the patronage of the independent sultans, bangla languageand literature were revived in the 15th century. Under the influence of Sri chaitanya's vaisnavism, the six Goswamins, 64 Mohantas and many other Vaisnavas wrote innumerable books in sanskritand Bangla using the Bangla script. In srikrishnakirtan (14th century) and Vodhicharyavatar (15th century), Bangla script had more or less attained its present form.

Between the 16th-18th centuries, some Bangla letters underwent a few insignificant changes. In 1778 Charles Wilkins established the first Bangla printing press at Hughli with letters modelled after the handwritten letters used in old Bangla books of verses. The first Bangla book to be printed was nathaniel brassey halhed's A Grammar of the Bengal Language (1778). Letters made by Wilkins were used for the Bangla text in the book. During the 19th century, numerous printing presses were established, leading to a reduction in the production of manuscript books. Printing ended the further evolution of the Bangla script. As long as books were written by hand, there were variations in the shapes of the letters. The introduction of printing put an end to these variations, and Bangla script assumed its present form. Current technology has provided various fonts for Bangla script, but its basic form remains unaltered.

The Bangla alphabet consists of both vowels and consonants. There are eleven vowels such as অ, অা, ই and 39 consonants such as ক, খ, গ, ঘ, making a total of 50 letters. The vowels can be pronounced independently, but the consonants need the support of vowels to be pronounced. Unlike English, Bangla vowels are not always written in full, being replaced by their signs. The vowel A is considered to be part of every consonant if there is no other vowel or vowel sign. However, other vowels are necessary, appearing in their complete forms at the beginning of a word and represented by their signs thereafter. For example, অাম (অা + ম)৴, but জাম (জ + া + ম), with the vowel অা being represented by the vowel sign . - Kalpana Bhowmik

Source: www.Banglapedia.org