Campaign for Socialism (CfS) is an autonomous political organisation of Scottish Labour Party members and supporters who campaign for left-wing policies and candidates within the party. In 2016, CfS agreed to a joint membership scheme with Momentum, a UK-wide grassroots movement supportive of Jeremy Corbyn and his leadership of the Labour Party.

Momentum is a British left-wing political organisation which has been described as a grassroots movement supportive of the Labour Party; since January 2017, all Momentum members must be members of the party. It was founded in 2015 by Jon Lansman, Adam Klug, Emma Rees and James Schneider after Jeremy Corbyn's successful campaign to become Labour Party leader and it was reported to have between 20,000 and 30,000 members in 2021.