The Michigan Department of Transportation (MDOT) is a constitutional government principal department of the US state of Michigan. The primary purpose of MDOT is to maintain the Michigan State Trunkline Highway System which includes all Interstate, US and state highways in Michigan with the exception of the Mackinac Bridge. Other responsibilities that fall under MDOT's mandate include airports, shipping and rail in Michigan.

The predecessor to today's MDOT was the Michigan State Highway Department (MSHD) that was formed on July 1, 1905 after a constitutional amendment was approved that year. The first activities of the department were to distribute rewards payments to local units of government for road construction and maintenance. In 1913, the state legislature authorized the creation of the state trunkline highway system, and the MSHD paid double rewards for those roads. These trunklines were signed in 1919, making Michigan the second state to post numbers on its highways. The department continued to improve roadways under its control through the Great Depression and into World War II. During the war, the state built its first freeways. These freeways became the start of Michigan's section of the Interstate Highway System. Since the mid-1960s, the department was reorganized. It was renamed the Michigan Department of State Highways for a time. Further changes culminated in adding all modes of transportation to the department's portfolio. In August 1973, the department was once again renamed to the Michigan Department of State Highways and Transportation by executive order. The name was later simplified and shortened to that of today.

The first State Highway Department was created on July 1, 1905. The department was born out of the Good Roads Movement at the turn of the century. Bicycle enthusiasts as a part of the League of American Wheelmen pushed for better roads and streets. They also wanted to ensure that bicyclists could use these streets and roads free from interference from horsedrawn vehicles. This movement persuaded the Michigan State Legislature to form a State Highway Commission in 1892. Another law in 1893 allowed voters in each county to establish county road commissions. The attention of Michigan residents was turned to the good-roads movement by Horatio S. Earle, the first state highway commission. In 1900 he organized the first International Road Congress in Port Huron and even put together a tour of a 1 mi (1.6 km) macadam road. He even ran for the state senate in 1900 at the urging of the Detroit Wheelmen bicycle club.

The legislature set up a state reward system for highways and created the State Highway Department with an office of Highway Commissioner. Earle was appointed by Governor Aaron Bliss. This appointment and department were voided when the attorney general ruled the law unconstitutional. A constitutional amendment was passed in 1905 to reverse this decision. The department was formed, and Earle was appointed commissioner by Governor Fred M. Warner on July 1, 1905.

At first the department administered rewards to the counties and townships for building roads to state minimum specifications. In 1905 there were 68,000 mi (110,000 km) of roads in Michigan. Of these roads, only 7,700 mi (12,000 km) were improved with gravel and 245 mi (394 km) were macadam. The state's "statute labor system" was abolished in 1907. Under that system, a farmer and a team of horses could work on road improvements in place of paying road taxes. Instead a property tax system was instituted with the funding only for permanent improvements, not maintenance. The nation's first mile of concrete roadway was laid along Woodward Avenue between Six Mile and Seven Mile roads in Detroit. This section of street was 17 feet 8 inches (5.38 m) wide. Work began by the Wayne County Road Commission on April 2, 1909 and finished on July 4, 1909, at a cost of $13,354 (equivalent to $332,472 in 2024).

In 1913 voters elected Frank Rogers to the post of highway commissioner. This election was the first after the legislature made it an elective post. Automobile registrations surged to 20 times the level at the department's formation, to 60,438, and there were 1,754 mi (2,823 km) of roads built under the rewards system. Passage of the "State Trunkline Act" provided for 3,000 mi (4,828 km) of roadways with double rewards payments. Further legislation during the Rogers administration allowed for special assessment taxing districts for road improvements, taxation of automobiles based on weight and horsepower and tree-planting along highway roadsides. Another law allowed the commissioner to name all unnamed state roads. It also allowed for the posting of signage with the names and distances to towns.

The centerline was first invented in 1911 in Wayne County by Edward N. Hines, and saw its first implementation on a state highway in 1917 along the Marquette-Negaunee Road, then M-15 and now County Road 492 in Marquette County. That same year, the first stop sign was put in place and the country's first "crow's nest" traffic signal tower was installed in Detroit. This traffic light using red-yellow-green was developed by William Potts, a Detroit police officer. Michigan is also home to the first snowplow. This winter maintenance started during World War I to keep 590 mi (950 km) of strategic highways clear. In 1919 Michigan first signed the trunklines, the second state after Wisconsin to do so.

The first ferry service was started on July 1, 1923, linking Michigan's Upper and Lower peninsulas. The first gasoline tax was enacted in 1923 at the rate of $0.02/gal (equivalent to $0.37/gal in 2024), but vetoed by Governor Alex Groesbeck. It was later enacted effective in 1926. The highway commissioner was also given complete control over the planning and maintenance of the state trunklines. Construction switched to concrete or asphalt only instead of gravel and macadam with an increase in the gas tax in 1927. Highway construction in the 1920s earned Michigan national attention. The first trunklline completed in concrete was M-16 (later part of US 16). The road was built to a standard of 20 ft (6.1 m) and between 7–9 in (17.8–22.9 cm) thick. The current standard at the time was 16 ft (4.9 m) wide and 6 in (15.2 cm) thick. The 1920s were also busy for Michigan highways as Michigan developed the yellow-line center line to indicate no-passing zones for sight-restricted hills and curves. Roadside picnic tables, soil testing and aerial surveying of highways also debuted at this time. As MDOT historians put it, "the age of mud was over; the age of concrete was moving in.