The paper aims to reveal how geological fieldwork was conducted in the Portuguese Geological Survey during great part of the twentieth century. We will see that in the first decades field assistants played a key role in conducting fieldwork and special attention will be given to their training. During the 1940s, the Portuguese Geological Survey could only rely on the French geologist Georges Zbyzsewski to conduct fieldwork and he was responsible for the introduction of new practices. However, field assistants were still the heirs of the Survey early scientific tradition, so compromises had to be established between them and the new French geologist when conducting fieldwork. In the meanwhile, scientific collaborators from outside the institution also began to play a key role in conducting fieldwork. From the 1950s, several new elements were hired to become part of the Survey technical staff, especially geologists and field assistants. The growth of elements in the technical staff with different scientific background and past experiences regarding fieldwork led to the creation of teams with specific and particular characteristics. Developments in fieldwork in the Portuguese Geological Survey were closely linked to economic policies implemented by the Portuguese State during the period studied, therefore an analysis of this relationship will also be made.