The earliest records mention Thibaud I, Count of Blois, in the 10th Century. He founded a family that remained in power until 1230. It was at that time that the first stone castle surrounded by a bastion was erected. Of the many medieval remains, the best preserved is a tower on a terrace overlooking the Loire. In 1429, Joan of Arc went to Blois to seek the blessing of the Archbishop of Reims before embarking on her campaign against the English in Orleans. Prince Louis of Orleans, the son of King Charles V, lived in the castle for 25 years with a small court. His grandson, King Louis XII, decided to move to Blois, making it a royal town and capital of the kingdom.

With its four wings in different styles surrounding an inner court, the royal castle of Blois is a remarkable illustration of the development of French architecture from the 13th to the 17th Century. King Louis XII transformed the somber medieval fortress into a lavish and luminous castle. The wing he built in red brick and gray stone stands out with its Gothic exuberance. The king's equestrian statue adorns the façade above the entrance. Louis XII also had a Renaissance garden built; unfortunately, it was destroyed in 1890.

His successor and son-in-law, Francis I, built a new wing from 1515 to 1524. It is very different in style, with a marked Italian influence. The most prominent feature of the Francis I wing, a masterpiece of the French Renaissance, is the magnificent spiral staircase with three floors of balconies opening to the central court, and with fine sculptural decoration. The king's emblem, the salamander, can be seen sculptured in a dozen places on the façade. Francis I put together one of the largest libraries of his time in the castle. However, after the death of his wife, Queen Claude, he spent little time at Blois and had the library moved to the Fontainebleau Castle where it served as the basis for the National Library.