Trinamool Congress, Congress, BJP and Left Front constituents CPI(M), RSP and Forward Bloc have fielded candidates in all the seats.
The Trinamool Congress is contesting the byelections alone.
By-elections to Rezinagar in Murshidabad district and Englishbazar in Malda district were necessitated by defection from Congress to Trinamool Congress by sitting MLAs Humayun Kabir and Krishnendu Narayan Chowdhury respectively, who were later inducted into the Mamata Banerjee ministry.
In Nalhati in Birbhum district, by-poll was being held after Abhijit Mukherjee, the son of President Pranab Mukherjee, was elected to the Lok Sabha from the Jangipur Parliamentary seat.