A thaler or taler (/ˈtɑːlər/ TAH-lər; German: Taler [ˈtaːlɐ], previously spelled Thaler) is one of the large silver coins minted in the states and territories of the Holy Roman Empire and the Habsburg monarchy during the Early Modern period. A thaler size silver coin has a diameter of about 40 mm (1+1⁄2 in) and a weight of about 25 to 30 grams (roughly 1 ounce). The word is shortened from Joachimsthaler, the original thaler coin minted in Joachimsthal, Bohemia, from 1520.

While the first standard coin of the Holy Roman Empire was the Guldengroschen of 1524, its longest-lived coin was the Reichsthaler, which contained 1⁄9 Cologne Mark of fine silver (or 25.984 g), and which was issued in various versions from 1566 to 1875. From the 17th century a lesser-valued North German thaler currency unit emerged, which by the 19th century became par with the Vereinsthaler.

The thaler silver coin type continued to be minted until the 20th century in the form of the Mexican peso until 1914, the five Swiss franc coin until 1928, the US silver dollar until 1935, and the Austrian Maria Theresa thaler. These days thaler-sized silver coins are not in active circulation anymore, but are minted by various government mints as bullion or numismatic items for collectors. The current derivative of the name, dollar (first Spanish and now mostly English), also survives as the name of several modern currencies.

German taler is recorded from the 1530s, as an abbreviation of Joachimstaler. The silver mines at Joachimstal had opened in 1516, and the first such coins were minted there in 1518. The original spelling was taler (so Alberus 1540). German -taler means "of the valley" (cf. Neanderthaler) -- cognate with English "dale", which also means "valley". By the late 16th century, the word was variously spelled as German taler, toler, thaler, thaller; Low German daler, dahler. In 18th to 19th-century German orthography, Thaler became standard, changed to Taler in the 1902 spelling reform.

The name taler, thaler was soon used in compounds denoting various types of silver coins of thaler size, thus Reichstaler (1566), Silbertaler, Albertustaler (1612), Laubthaler (1726), Kronenthaler (1755), Ortsthaler, Schützentaler, Bankthaler, Speciethaler, etc.

Units used in the Netherlands include the daalder, the rijksdaalder and the leeuwendaalder. From 1754, many German states used the Conventionsthaler as well as a lower-valued North German thaler or Reichsthaler worth 3⁄4 the Conventionsthaler. From 1840 the various North German thalers converged to the value of the Prussian thaler and afterwards the Vereinsthaler.

The corresponding English silver coin of the period was the crown. The Low German word was adopted in English as daler by 1550, modified to dollar by about 1600. English thaler was introduced in the first half of the 19th century to refer to the coins of the German states, as the word dollar was increasingly understood to refer to the United States dollar.

The development of large silver coins is an innovation of the beginning Early Modern period. The largest medieval silver coins were known as groat (German Groschen), from denarius grossus or "thick penny". These rarely exceeded a weight of 6 grams.