The term "half-timbered walls with earth infill" refers to a wide number of techniques in which structural wooden elements are combined with enclosures made of earth. The use of these constructive systems dates back to prehistoric times and their evolution has differed based on the physical, social and cultural conditions of each place. Therefore, the objective of this paper is to define the concept of half-timbered walls with earth infill in the Spanish context and to understand the geographical, urban, architectural and constructive reasons that have favoured or hindered its use in traditional architecture. The methodology used is based on the quantitative and qualitative analysis of the largest possible number of case studies. This allows a database to be set up for the purposes of performing global analysis and drawing objective and statistically valid conclusions. This information is managed using a study sheet with information ranging from general aspects of buildings with the presence of these techniques to detailed features of half-timbered walls. The data and conclusions presented in this paper focus on these half-timbered walls, including information on the geographical distribution of these techniques, the characteristics of the buildings in which they are used, the combination of mixed walls with other construction techniques, and the state of conservation and transformation of the buildings in which they are used. It has been established that these techniques are common in mountainous landscapes, where there is optimal woodland for construction, and in urban environments, where they are presented as optimum techniques to maximize the profitability of the buildable surface.