Lexicography and applied linguistics are broad fields with multiple disciplinary affiliations, which certainly overlap in the 20th and 21st centuries. Both are heterogeneous domains of intellectual activity through contact with other disciplines. For dictionary-makers, lexicography has long been a kind of professional practice. According to the Oxford English Dictionary, lexicography involves "the writing or compilation of a lexicon or dictionary; and the art or practice of writing dictionaries", and the latter quoted from Johnson. The institutional and commercial constraints within dictionary publishing were nevertheless tackled during the twentieth century by two outstanding individuals in English and Spanish lexicography, whose work was grounded in decades of professional practice outside lexicography. The Oxford Advanced Learner's Dictionary of Current English (OALD) marked a very substantial shift in English lexicography. The elevation of the user perspective in functional theories of lexicography shows how lexicographic principles are readily extrapolated from lexicographic practice.