Altheim (German pronunciation: [ˈaltˌhaɪm]) is a municipality in the district of Alb-Donau in Baden-Württemberg, Germany.

In the 13th century, Altheim was a possession of the Lordship of Steußlingen. The township was mediatized to the Kingdom of Württemberg in 1805 and it was assigned to Oberamt Urspring [de]. Altheim was reassigned to Oberamt Ehingen [de] in 1810 and remained in that district when it was reorganized in 1938 into Landkreis Ehingen [de]. After World War II, Altheim, still a haufendorf with two separate town centers, began an urban spread to the west. As part of the 1973 Baden-Württemberg district reform [de], Ehingen's district was dissolved and Altheim was assigned to the new Alb-Donau district.

Altheim is a municipality (Gemeinde) of the Alb-Donau district of Baden-Württemberg, one of the 16 states of the Federal Republic of Germany. It is physically located in the Hochsträß [de] region, so named for a historic road that runs through the municipality from west to east. Elevation above sea level in the municipal area ranges from a high of 640 meters (2,100 ft) Normalnull (NN) to a low of 550 meters (1,800 ft) NN where the Siegentalgraben flows into the Schmiechener See [de].

Altheim's coat of arms displays three plates upon a field of blue. At the top of the blazon is a white chief and upon that a blue, engrailed and invected line. This coat of arms was first adopted by the municipal council of Altheim on 3 March 1937 with permission from its owner, Baron Conrad von Freyberg, head of a local noble house that had lived in the area since 1528. A request to for approval of official use of this coat of arms was sent to the Reichsstatthalter of Württemberg, though approval did not materialize. A modified version was used through World War II, with the field behind the roundels was turned black and a yellow chief containing a black stag antler. On 24 August 1957, the Federal Ministry of the Interior approved the Freyberg coat of arms, but changed the chief to its current state as a reference to Altheim's 13th century owners, the Lords of Steußlingen. A municipal flag was issued alongside the official coat of arms.