Montana voters approved Initiative 128 in 2024, establishing a state constitutional right to abortion before fetal viability. The measure passed with 58 percent in favor and 42 percent opposed. Voters rejected Initiatives 126 and 127; Initiative 126 proposed top-four primaries and was defeated with 51 percent opposed, while Initiative 127 would have required a majority rather than a plurality to win certain state and federal offices and was defeated with 60 percent opposed.

Montana voters have decided on three abortion-related ballot measures. In 2012, voters approved a measure requiring parental notification for minors seeking abortions with 71 percent approval. Voters rejected Legislative Referendum 131 in 2022, which would have granted legal personhood to infants born alive and required medical care for them; the measure failed with 47 percent in favor and 53 percent opposed.

Montana voters authorized the initiative and referendum process by approving a constitutional amendment in 1906, making the state the fifth in the U.S. to adopt such a process. Voters ratified their current state constitution in 1972, which passed by a margin of approximately one percentage point, following approval of Referendum 67 in 1970 authorizing a constitutional convention.

In 1904, voters approved an eight-hour workday limit for mills, smelters, and mines with a 77 percentage point margin and a measure prohibiting employment of children under 16 in underground mines with an 85 percentage point margin. This was extended in 1936 when voters approved a constitutional amendment covering all industries.

Voters approved a 1934 constitutional amendment establishing graduated and progressive income taxes, with revenue allocated to public schools and state government. Montana does not have a general statewide sales tax; voters rejected sales taxes in 1971 and 1993, and approved a 1994 amendment limiting future statewide sales or use tax to 4 percent.

Voters approved a 1996 measure prohibiting corporate contributions to ballot-measure campaigns. The Montana State Legislature passed House Bill 575 in 1997 expanding this ban, which voters upheld through a 1998 veto referendum before a court struck down the restrictions. A 2012 initiative banning corporate contributions was approved but overturned by a court in 2013.

Initiative 64 established term limits in 1992 for statewide executives, legislators, and members of Congress. Voters approved Initiative 96 in 2004 defining marriage as between one man and one woman; this amendment was invalidated by a 2015 U.S. Supreme Court ruling. Voters rejected a 2004 amendment to increase state legislative term limits.