Today, there is consensus on the idea that corpora are the natural habitat of terms or, in other words, the backbone of terms. Thus, it seems that in vivo terminological work is the most 191appropriate in different contexts, such as in the translation of specialized texts, in the elaboration of terminological dictionaries or in terminological standardization, among others. The constitution of specialized corpora is, therefore, indispensable to carry out all the necessary tasks related to terminological work. For the elaborated corpora to be adequate, it is necessary to take the different criteria for the constitution of specialized corpora and their typology into account, which will vary depending on the objective of the work. Likewise, it is fundamental to understand the notion of terminological unit to be able to identify and select the terminological units in specialized corpora. These corpora are also a very valuable source to extract information associated with the terms, such as variants (synonyms or acronyms, for example), definitions, real use contexts or specialized phraseology. In order to facilitate the tasks related to the methodology of terminological work, currently, automatic tools and resources are used, such as systems for the selection of specialized texts, terms (or terms candidates) extractors and, terminological databases. All these aspects will be dealt with in detail in this chapter, taking the Spanish language as the starting point.