Scottish National Party leader Humza Yousaf quits, triggering a search for a successor and new first minister.
He said he had "underestimated" the level of hurt after ending a power-sharing deal with the Scottish Greens last week.
Mr Yousaf says he will stay on as first minister until the SNP chooses his replacement.
Opposition parties in the Scottish Parliament have tabled two confidence votes - one in the first minister and another in the SNP government.