In February 2002, National Grid Group acquired Niagara Mohawk, an electricity and gas utility in New York state.

In October 2002, National Grid and Lattice merged to form National Grid Transco (in 2005, the Company reverted to National Grid).  A number of small, non-core UK businesses have been divested since the merger.

On 1st September 2004, National Grid acquired the UK wireless infrastructure network of Crown Castle International Corporation. 

On 1 June 2005, National Grid completed the sale of four gas distribution networks in the UK.

In September 2006, National Grid completed the acquisition of Rhode Island Gas.

During 2007, National Grid sold of National Grid Wireless, Basslink and Advantica.

On 24 August 2007, National Grid completed the acquisition of KeySpan Corporation.