| Election Name: | 1966 Hessian state election |
| Country: | Hesse |
| Type: | parliamentary |
| Ongoing: | no |
| Previous Election: | 1962 Hessian state election |
| Previous Year: | 1962 |
| Next Election: | 1970 Hessian state election |
| Next Year: | 1970 |
| Seats For Election: | All 96 seats in the Landtag of Hesse |
| Majority Seats: | 49 |
| Election Date: | 6 November 1966 |
| Turnout: | 2,868,446 (81.0% 3.2pp) |
| Candidate1: | Georg-August Zinn |
| Party1: | Social Democratic Party of Germany |
| Last Election1: | 51 seats, 50.8% |
| Seats1: | 52 |
| Seat Change1: | 1 |
| Popular Vote1: | 1,442,230 |
| Percentage1: | 51.0% |
| Swing1: | 0.2pp |
| Candidate2: | Alfred Dregger |
| Party2: | Christian Democratic Union of Germany |
| Last Election2: | 28 seats, 28.8% |
| Seats2: | 26 |
| Seat Change2: | 2 |
| Popular Vote2: | 745,409 |
| Percentage2: | 26.4% |
| Swing2: | 2.5pp |
| Candidate3: | Heinrich Kohl |
| Party3: | Free Democratic Party (Germany) |
| Last Election3: | 11 seats, 11.4% |
| Seats3: | 10 |
| Seat Change3: | 1 |
| Popular Vote3: | 293,394 |
| Percentage3: | 10.4% |
| Swing3: | 1.0pp |
| Candidate4: | Heinrich Fassbender |
| Party4: | National Democratic Party of Germany |
| Last Election4: | Did not exist |
| Seats4: | 8 |
| Seat Change4: | 8 |
| Popular Vote4: | 224,674 |
| Percentage4: | 7.9% |
| Swing4: | New |
| Party5: | GDP |
| Color5: | C3C318 |
| Last Election5: | 6 seats, 6.3% |
| Seats5: | 0 |
| Seat Change5: | 6 |
| Popular Vote5: | 121,326 |
| Percentage5: | 4.3% |
| Swing5: | 2.0pp |
| Map Size: | 250px |
| Government | |
| Before Election: | Fourth Zinn cabinet |
| Before Party: | SPD–GDP |
| Posttitle: | Government after election |
| After Election: | Fifth Zinn cabinet |
| After Party: | SPD |
The 1966 Hessian state election was held on 6 November 1966 to elect the 6th Landtag of Hesse. The outgoing government was a majority of the Social Democratic Party (SPD) and All-German Party (GDP) led by Minister-President Georg-August Zinn.
The SPD retained its majority and remained stable on 51%. The opposition Christian Democratic Union (CDU) slipped to 26%, and the Free Democratic Party (FDP) 10%. The GDP, which had been in government with the SPD since 1955, fell to 4% and lost its representation in the Landtag. In its place the new radical right-wing National Democratic Party (NPD), led by former FDP politician Heinrich Fassbender, won 8% and 8 seats. This marked the party's first entry into a state parliament and attracted great attention and concern both domestically and internationally. After the election, the SPD chose to govern alone and Minister-President Zinn continued in office.
The Landtag was elected via mixed-member proportional representation. 48 members were elected in single-member constituencies via first-past-the-post voting, and 48 then allocated using compensatory proportional representation. A single ballot was used for both. An electoral threshold of 5% of valid votes is applied to the Landtag; parties that fall below this threshold are ineligible to receive seats.
See main article: 1962 Hessian state election. In the previous election held on 11 November 1962, the SPD won an absolute majority of both votes and seats for the first time. This came to the detriment of both the CDU and GDP. Despite being able to govern alone, the SPD retained the GDP in its coalition.
The table below lists parties represented in the 5th Landtag of Hesse.
| Name | Ideology | Lead candidate | 1962 result | |||||
|---|---|---|---|---|---|---|---|---|
| Votes (%) | Seats | |||||||
| bgcolor= | SPD | Social Democratic Party of Germany | Social democracy | Georg-August Zinn | 50.8% | |||
| bgcolor= | CDU | Christian Democratic Union of Germany | Christian democracy | Alfred Dregger | 28.8% | |||
| bgcolor= | FDP | Free Democratic Party | Classical liberalism | Heinrich Kohl | 11.4% | |||
| bgcolor=#C3C318 | GDP | All-German Party | National conservatism | 6.3% | ||||