Participation in Maine's delegate selection process is open to all registered voters who are enrolled in the Democratic Party. A resident may register to vote on the day of the caucus.

Sunday 6 March 2016: Maine Municipal Caucuses. Hours 1:00p-6:00p EST (1800-2300 UTC). Delegate Pledging: Proportional Caucus/Convention. Voter Eligibility: Closed Caucus/Convention.

Municipal Caucuses
Source: WMTW ABC Portland.
Status: Unofficial. Retrieved: Wednesday 9 March 2016.
Excluded from Nationwide vote.

Sunday 6 March 2016: The Municipal Caucuses meet to choose delegates to the State Convention. The State Convention delegates are allocated to presidential contenders in proportion to the percentage of the support each candidate receives at the Municipal Caucus.

"Municipal Caucuses will determine the apportionment of delegates to the State Convention based on ... presidential preference .... In turn, the apportionment of delegates to the National Convention will be determined by presidential preference ... at the State Convention." [Maine Delegate Selection Plan. Section I. B.2.]

Municipal Caucus (estimate)
National Convention Delegate Estimate
Source: WMTW ABC Portland.
Status: Unofficial. Retrieved: Wednesday 9 March 2016.

Friday 6 May - Saturday 7 May 2016 (presumably): State Convention. 25 of 30 delegates to the Democratic National Convention are allocated to presidential contenders based on the presidential preference of the delegates in attendance at the State Convention. A mandatory 15 percent threshold is required in order for a presidential contender to be allocated National Convention delegates at either the congressional district or statewide level. How the Democratic Proportional Delegate Allocation Math works.

• 17 district delegates are to be allocated proportionally based on the delegates presidential preferences in each of the State's 2 congressional districts.
• In addition, 8 delegates are to be allocated to presidential contenders based the support for the presidential contenders in the State Convention as a whole.
• 5 at-large National Convention delegates
• 3 Pledged PLEOs

7 May 2016 update Maine Democrats torn between Sanders, Clinton at state convention from the Bangor Daily News. "... is choosing delegates — 17 for Sanders and 8 for Clinton ... to represent Maine at the National Democratic Convention in Philadelphia in July."

Maine Democrats Energized by 2016 State Convention ... state delegates elected Maine’s 25 pledged delegates, 17 of which were allocated for Sen. Bernie Sanders, and 8 of which will go to Secretary Hillary Clinton ... The national delegates elected for Sen. Sanders were: Diane Denk, Vanessa Sylvester, Liz Smith, Todd Ricker, Seth Berner, Justin Beth, Cokie Giles, Cynthia Soma-Hernandez, Jesse Lambert, David Bright, Ursa Beckford, Severin Beliveau, David Weeda, Denise Groves, former state Rep. Harlan Baker, state Rep. Diane Russell and state Rep. Deane Rykerson. ... The national delegates elected for Secretary Clinton were: Cynthia Dill, Nancy Wanderer, Margaret Hannah, Trevor Doiron, Dale McCormick, Ralph Carmona, state Rep. Chris Babbidge and Maine Attorney General Janet Mills.

State Convention
Source: Maine Democrats Energized by 2016 State Convention.
Status: Official. Retrieved: Tuesday 17 May 2016.

National Convention delegates are elected at the state Convention.

The remaining 5 National Convention delegates consist of

• 5 Unpledged PLEO delegates:
• 4 Democratic National Committee members.
• 1 Member of Congress (0 Senators and 1 Representative).
• 0 Governors.
• 0 Distinguished Party Leaders.

These 5 delegates and will go to the Democratic National Convention officially "Unpledged".

Maine state Representative Deane Rykerson (Democratic) sponsored LD 1422 circa 23 April 2013. The bill sets the date of Maine's Presidential primary to be no earlier than 1 January and at either a date determined by the political parties, 1 week after the New Hampshire primary, or the first Tuesday in March.
The bill received a vote of no confidence from the Joint Committee on Legal and Veterans Affairs on 13 May 2013.

Details of the bill:

• A presidential primary election ... may not be held earlier than January 1st.
• Whenever ... a party ... has voted to conduct a presidential primary ... the State shall hold a presidential primary election .... The party shall deliver ... notification of the chosen date by December 1st of the year prior to the presidential election year.... If ... more than one party and those parties agree by November 1st of the year prior to the presidential election year to one date, the State shall hold the presidential primary election on that agreed-upon date.
• If a party does not choose a date ... or there is no agreement on a date ... the State shall hold the presidential primary ... on the first Tuesday after the presidential primary election in New Hampshire, unless that primary occurs in the preceding calendar year, in which case the election must be held on the first Tuesday in March.