Issues which could prove divisive at Stormont talks table
Northern Ireland is currently the only part of the UK and Ireland where same-sex marriage isn't legal. Sinn Fein wants to change this, but the DUP is virulently opposed. Same-sex marriage actually had a majority at Stormont when it was voted on for a fifth time in November 2015, but the DUP blocked it.
Irish Language Act
Sinn Fein wants legislation for a 'stand alone' Irish Language Act, which the DUP opposes. This has become a bitter division point, and highly symbolic of the cultural war that exists between Sinn Fein and the DUP.
The Petition of Concern
The reason why the DUP has been able to veto same-sex marriage is because it has used the Petition of Concern. This mechanism is supposed to be used to safeguard minority rights, but has been used questionably in the past by both main parties. The SDLP has called for a temporary suspension of the Petition of Concern to allow the Assembly to pass policies which enjoy majority support but which the DUP would block. Neither Sinn Fein nor the DUP seem keen on removing the veto, but some reform of it could be possible.
The RHI inquiry
The report of the inquiry into the botched green energy scheme is expected within months, and could be damning for Arlene Foster. But it could also provide a wider critique of how Stormont operates.