Five Scottish Labour politicians joined the contest for leader and deputy leader of the party on the first day nominations opened.
MSPs Kezia Dugdale and Ken Macintosh will fight for the leadership role.
Glasgow City Council leader Gordon Matheson and MSPs Alex Rowley and Richard Baker will battle it out for the deputy leader post.
The elections were sparked after leader Jim Murphy and his deputy Ms Dugdale resigned from their positions.
The changes at the top of the Scottish party come in the wake of Labour losing all but one of its 41 seats at May's general election.
On Monday, Ms Dugdale said she had secured backing from 30 of the Scottish Labour Party's 40 parliamentarians.
She added: "My campaign will be reaching out to people whose support Labour has lost, and those who've never voted for us before - because our values are as relevant today as they have ever been."
Mr Macintosh, who is MSP for Eastwood, said the election was a "terrible defeat" for Labour.
He added: "Scottish Labour needs to become more open, more transparent and we must shift control of our party from the corridors of power to the communities of Scotland - I believe a healthy, robust leadership contest which listens to Scotland will start that process."
Council leader Mr Matheson said he believed he had the necessary experience to take on the deputy leader role.
He said: "The Scottish Labour Party needs to stop feeling sorry for itself and instead focus on the concerns of the people of Scotland.
"I offer the distinct combination of experience and change. I have successfully led Scotland's largest city for over five years. But because I'm not an MSP I offer a fresh perspective on the national political scene."
Mr Baker said he was aware of the scale of the challenge facing Labour and said he wanted to play his part in overcoming those challenges.
He added: "I am looking forward to meeting members across the country over the coming weeks to discuss how we can work together to rebuild our great party."
Following changes spearheaded by Mr Murphy before his departure at the weekend, the election for both the leader and deputy leader will be based on one-member-one-vote.
To stand as leader, candidates must already have been elected as an MP, MSP or MEP.
Candidates for deputy must already have been elected an MP, MSP, MEP or councillor.
To stand as deputy, candidates must achieve at least 15% of support from the elected parliamentary group, which includes MSPs, Labour's sole Scottish MP Ian Murray and MEPs, or 15% of Scottish Labour councillors.
All the contestants will take part in a series of hustings at four venues including;
- Edinburgh - Monday 22 June
- Glasgow - Wednesday 24 June
- Aberdeen - Friday 26 June
- Dundee - Monday 29 June
The results of the two contests will be announced at a special gathering on Saturday 15 August.
15 June - Nominations open for leader and deputy leader
19 June (12 noon) - Nominations close
19 June (17:00) - Supporting nominations open
22 June - Hustings period opens
13 July - Last date to join as member, affiliated supporter, or registered supporter in order to vote in the leadership ballot
10 July (12 noon) - Supporting nominations close
20 July - Ballot opens
14 August - Ballot closes
15 August - Result announced