Gray, Virginia, Russell L. Hanson, and Herbert Jacob, eds. 1999. Politics in the American States: A Comparative Analysis, Seventh ed. D.C.: CQ Press, p. 88; updated by Gary Keith.

Footnote 1: Party registration is required.
Footnote 2: Voters may register or change registration on election day. In Iowa, Ohio and Wyoming, voters may change registration on primary election day. In California, Massachusetts and New Hampshire voters may register with a party on primary election day. And in Colorado, Kansas, Maine, New Jersey and Rhode Island voters who have not previously voted in a party primary may change their registration on primary election day.
Footnote 3: Public selection of a party is required.
Footnote 4: Voters may vote in any party's primary.
Footnote 5: Voters may vote in more than one party's primary, but only for one candidate per office. This method was declared unconstitutional, though litigation, legislation, and ballot measures in the former blanket primary states of Alaska, California, and Washington continue to keep their systems in flux.
Footnote 6: The top two primary vote getters, regardless of party, are nominated for general election.