This work presents a study of the oldest Acheulean lithic assemblages from the Galería site, specifically the GIIa subunit, which has been dated to c. 503 ± 95 ka, and compares them with the subsequent subunit in the sequence, GIIb, dated to around 237–269 ka. The main goals of this study are to offer a detailed technological characterization of the earliest Acheulean presence in Atapuerca and to assess the elements determining the technological variability in a given site by studying the sequence, evaluating the concept of variability and defining the aspects which determine it. The Galería site does not display the features of a living space. It is a cave which was accessed by both humans and carnivores in order to obtain the animal biomass of the herbivores that had fallen down into the cave through a natural shaft. The archaeological record is therefore incomplete and fragmented, since it is the product of highly changeable occupational dynamics. In the lower Galería levels, we identified the development from an almost exclusive use of cobbles as blanks for knapping activities in the earliest periods to an increasing use of flakes. In terms of raw materials, the initially predominant use of Neogene chert and quartzite evolved towards a more balanced use of six raw materials. Furthermore, there was an increase in the size of the large tools. After comparing these two Acheulean assemblages, it is important to put them into context by taking into account a) the significance of cobbles and flakes as blanks; b) the significance of cleavers; and c) the use of raw materials such as quartzite, sandstone or chert. These aspects have traditionally been used to facilitate comparisons of the technologies used within the Iberian Peninsula, and comparisons between the Acheulean technology of the Iberian Peninsula and North Africa and the European (i.e. trans-Pyrenean) Acheulean technology.