Mahishya (IAST: Māhiṣya) is a Bengali Hindu traditionally agrarian caste, and formed the largest caste in undivided Bengal. Mahisyas were, and still are, an extremely heterogeneous caste, encompassing all possible classes in terms of material conditions and ranks — ranging from a majority of small farmers and working class individuals to a significant section of landed magnates and industrial entrepreneurs.

The Kalaikuri-Sultanpur copperplate inscription of 439 CE brings to light the presence of Kaivartaśarman, a Brahmin Kuṭumbin (peasant landholder) in the local administration (adhikaraṇa) in Varendra of Gupta period. There are references to vṛttis (enclosed land) in same administrative unit like Osinnakaivartavṛtti, Uddhannakaivartavṛttivahikala, in the copperplate inscriptions of Mahīpāla I. Historian Ryosuke Furui suggests this as the probable location of the leader of Samantas who revolted against the Pala regime. In one inscription of Madanapala, Kaivarta was assigned vritti in royal estate along with Buddhist establishment and Carmakāra. In one plate of Gopala II, kaivartta was listed as one of the lowest categories of the rural society. It makes a striking contrast with the references to kaivartta in the later inscriptions and the Råmacarita, which rather show their higher social position. Furui notes this ‘shift’ may mean the upward social mobility of a part of kaivarttas. Otherwise it shows some diversity within a social group labelled as 'kaivartta'.

According to 13th century text Brihaddharma Purana, children of Shudra fathers and Kshatriya mothers are dāsa, an Uttam Sankar (literally, good mixed) and their occupation is agriculture. According to the Brahma Vaivarta Purana, whose chapter describing mixed castes was likely inserted after 16th century, Kaivarta was one born of a Kshatriya father and a Vaishya mother. Some ancient or mediaeval texts like Yājñavalkya Smṛti and Gautama Dharmasutra give identical parentage, that is, one born to a Kshatriya father and a Vaishya mother for Mahishya, who was supposed to be engaged in the profession of astronomy or agriculture. The late sixteenth century text Chandimangal mentioned one group of Dāsas, who were cultivators. The term 'Chasi-Kaibarta' first appeared in Bharatchandra Ray's Annada Mangal (1753).

In 19th century various groups from different regions of Bengal were known by the names like Uttar-rarhi Chasi-Kaibrtta, Dakshin-rarhi Tunte Kaibartta (mulberry planters and silk traders), Purba-desi Kaibartta (cultivators), Das or Chasi/Haliya Das, Siuli (date tappers), Mala or Jele (fishers) etc.; substantial majority of them later consolidated and identified as Mahishya.

According to Niharranjan Ray many Kaibartas held posts of administrators and legal officers from eighth to thirteenth century. Jyotirmoyee Sarma, another historian, observes that many Kaivartas, alternately with many Brahmins, acted as ministers in Pala royal courts, such as Yasodasa, who held a position of prime importance at the court of Rajyapala. In eleventh century, in a rebellious hostility, Divya, originally a feudal chief (Samanta) of Kaibarttas, killed Mahipala II, seized Varendra and established a regime there, which was ruled by him, his brother Rudok and nephew Bhima for around half a century. R. C. Majumdar interpreted it as a rebellion of local Samantas. Romila Thapar suggests that this is perhaps the first peasant rebellion in Indian history. Ram Sharan Sharma states that in his rule Bhima dispossessed the brahmanical and other beneficiaries and levied taxes from them, and prioritised the interests of the peasants. Ray also notes that some of the Kaibartas were well versed in Sanskrit and composed poetry during the eleventh and twelfth centuries.

At the start of the 18th century, the Bengali society had solidified into a definite structure with the three upper castes of Bengal having a collective hegemony over the "Bhadralok samaj", though prominent individuals from some other middle ranking castes including Mahishyas, who had acquired sufficient education, fame and prosperity were also undoubtedly considered as Bhadralok. In fact, Mahishyas, in general, tried their best to align themselves with the Bhadralok image in order to achieve upper social mobility.

At the end of 19th century scholars appeared to differ on the rank of the Mahisyas in Bengali society. Sankritist and antiquarian, Rajendralal Mitra appeared to believe that Mahisyas were a caste of small farmers and could not afford forces of modernity such as school education. But the president of the college of Nadia pandits, Jogendranath Bhattacharya, who published a major book "Hindu Castes and Sects" in 1896, wrote that in the Tamluk and Contai subdivisions of Midnapore, where population of high castes was very small and Kaibarttas were very numerous, they may be reckoned among the local aristocracy and in other districts their position was next only to the Kayasthas. In 1864, the first decree (Byabasthāpatra) was taken from 64 Brahmin scholars in Bikrampur, Dhaka to increase the community's social status. With the encouragement and patronage of Krishna Chandra Roy, the Zamindar of Nannur, Dhaka, Basanta Kumar Roy wrote the first book on Mahishya name claim - "Mahishya Bibriti" in around 1890. The Mahishya movement during the late nineteenth century was the work of successful men who had seized the new avenues of power opened by commerce, education and professions. Whereas the samajpatis, who as substantial landholding families (such as Tamluk and Moyna families) had from generation to generation stood as the social leaders of different local samajs of the Kaibartta community, were generally opposed to the movement.

Till then all these individuals were known as Chasi-kaibartta which was an incredibly diverse caste. The Chasi-kaibartta, who numbered more than half of the population in eastern and southern parts of Midnapore, reclaimed the culturable wastelands and thus secured for themselves during the days of Mughal faujdars a dominant position in the agrarian economy, filling up all the strata - zamindars, jotedars or rich farmers, small peasants down to share-croppers and agricultural labourers. Some royal families of Medinipur such as the Tamluk Raj family, the Kajlagarh Raj family and the Moyna Raj family identified themselves as Mahishyas. In the district of Dhaka all the upper and middle classes of Mahishyas, who were also known as Parasar Das or Halik Das, were zamindars and substantial landholders from the time of Muslim rule. In the districts like Burdwan, Hooghly, Nadia and the 24 Parganas or in the eastern areas like Faridpur, they enjoyed an important position in agriculture, some of them being substantial landholders, grain-dealers and peasant-proprietors. In some subdivisions of south-western Bengal, many families made fortune by silk production, salt production and trade. There were some major landed families in Calcutta such as Marh family in Janbazar and the Mondal family of Bawali in Tollygunge In the city there was a large mahishya contingent working as traders, manufacturers and professionals like lawyers, engineers and doctors.