Political leaders welcome Arlene Foster as new First Minister
The Prime Minister has joined other political leaders in wishing Arlene Foster well as Northern Ireland's new First Minister.
David Cameron said he looked forward to working with the Democratic Unionist leader.
Irish Taoiseach Enda Kenny and Scotland's First Minister Nicola Sturgeon also congratulated Mrs Foster on her appointment.
The Fermanagh and South Tyrone Assembly member has taken over from the retiring Peter Robinson.
Mr Cameron tweeted: "Congratulations to Arlene Foster, NI's 1st female First Minister. I look forward to working with her on a positive future for NI."
Ms Sturgeon said: "Congratulations to Arlene on her appointment and I wish her well in the role.
"It's heartening to see another female first minister and I look forward to working with her and Deputy First Minister Martin McGuinness on issues where we have a common goal and purpose.
"Of course, she follows Peter Robinson, who was a formidable leader and someone who I have enjoyed getting to know during our time in office."
A spokesman for Mr Kenny said the Taoiseach wished the "highly effective" Mrs Foster "every success in her new role".
"He looked forward to continuing to work with her to meet challenges and develop opportunities to benefit all communities across the island of Ireland," he said.
The spokesman added: "The Taoiseach also paid tribute to Ms Foster's predecessor Peter Robinson, thanking him for his very significant contribution to the Northern Ireland peace process and wishing him many happy years of retirement with his family as he stepped down as first minister."