William H. Horstmann & Co. (later Horstmann Brothers and Company) was a manufacturer and retailer of civilian and military equipment, including military uniforms, insignias, and flags. The company was established in 1815 by William H. Horstmann (1785-1850), a native of Cassel, Germany. He learned the trade of silk-weaving in France, and upon emigrating to the United States, established himself in Philadelphia as a manufacturer of fringe, laces, and trimmings of various kinds.

In 1828, the company began the manufacture of military trimmings. The company consisted of two branches: one dealt in civilian clothing and goods, and the other in military uniforms and equipment. The company executive large government contracts for the War and Navy Departments.

After his sons, William H. Horstmann (1819-1872) and Sigmund H. Horstmann (1821-1870) joined the firm, they established another branch of the business in New York, New York in 1831. Factories were built, first at the corner of Germantown road and Columbia avenue, and later on Fifth street and Cherry street, both in Philadelphia.

The firm was known by a variety of names: William H. Horstmann & Sons (1843-1893, Philadelphia), Horstmann Brothers & Company (1850-1852, New York; 1859-1893, Philadelphia), Horstmann Brothers & Allien (1852-1877, New York), Horstmann Sons & Drucker (1845-1849, New York), and the William H. Horstmann Co. (1893-1940, Philadelphia).