Thousands of students face disruption as staff at more than 40 universities join picket lines across the UK.
It is part of a long-running dispute by members of the University and College Union (UCU) over pay and conditions.
The action will be smaller than planned as dozens of branches called off action following constructive talks with their universities.
The Universities and Colleges Employers Association (UCEA) says this year's pay deal is the highest offer in 20 years.
But the union is calling for an above-inflation pay rise and an end to insecure contracts.
