The key feature of Urquijo's work is its great multifariousness, as his contribution falls into a number of areas: general linguistics, comparative linguistics, paremiology, onomastics, ancient songs and stories, origin of the Basque language, folklore, archaeology, heraldry, etymology, music, literature including poetry, invented universal languages and commercial history of Bilbao, not to count single pieces representing odd and isolated subjects. Another fundamental characteristic is scholarly discipline, especially as opposed to sometimes extravagant and highly hypothetical theories pursued by other vascophiles of the early 20th century. Though initially Urquijo displayed interest in some very specific topics like evolution of the Sare dialect, over time he specialized in two areas. The first one was bibliography, which suited his systematic nature and together with periodical accounts supplied to "RIEV" made him emerge as "mayor bibliografo vasco". Another one was paremiology, always generating his particular interest and resulting in a number of publications. Some works add also dialects and their changes over time as another of his preferred subjects. In terms of own writings, Urquijo's contribution was incomparable to production of Azkue, especially that his knowledge and fluency in Basque was far inferior. Contemporary scholars summarise his work as discreet and modest but effective, possibly constrained by his excess self-criticism; they rush to underline that in general, apart from his scholarly production and organizational achievements, Urquijo's contribution consisted to a huge extent of discussion and friendly critique. Some vascólogos even consider his polemical effort as one of key threads of his entire activity, pointing that he did not refrain from and indeed willingly engaged in always amicable disputes with , Baroja and many others. As a vascólogo Urquijo was involved in a number of fundamental debates related to the Basque realm. He followed Azkue when confronting the "aranistas". He charged them with pursuing an amateurish and highly speculative approach, resulting in advancing theories which suited their allegedly idealized, Arcadian and almost mythical vision of Basque community; this stance had to be repelled by purely scientific approach. Urquijo's decisiveness in dismantling what he considered myths has even earned him the opinion of an iconoclast. Another line of conflict with the Aranists was their perceived obsession with linguistic purity, entangled in "extravagant etymologies" and "most grotesque hypotheses"; one of the SEV objectives was to wrest the language issue away from zealous nationalists, especially that Urquijo personally appreciated internal variability of Basque dialects.