Books on Universals · Anthony Nuñez

One great starting point

Michael J. Loux — Metaphysics: A Contemporary Introduction (4th ed.)
Clear, even-handed chapters on the Problem of Universals (realism, conceptualism, nominalism) with up-to-date bibliographies.
Link: https://www.routledge.com/Metaphysics-A-Contemporary-Introduction/Loux/p/book/9781138639348(Routledge)

D. M. Armstrong — Universals and Scientific Realism (Vol. 1: Nominalism & Realism; Vol. 2: A Theory of Universals)
The classic defense of immanent realism about universals; Vol. 1 also surveys rival views.
Links:
Vol. 1 Cambridge page: https://www.cambridge.org/sj/universitypress/subjects/philosophy/philosophy-general-interest/nominalism-and-realism-universals-and-scientific-realism-volume-1 (Cambridge University Press & Assessment)
Internet Archive record: https://archive.org/details/universalsscient0000arms (Internet Archive)
D. M. Armstrong — Universals: An Opinionated Introduction (1989)
Short, crisp map of the main positions (realism, nominalisms, trope theories) with Armstrong’s preferred take.
Links: https://archive.org/details/universalsopinio0000arms (Internet Archive) • https://www.amazon.com/Universals-Opinionated-Introduction-D-Armstrong/dp/0813307724 (Amazon)

Gonzalo Rodriguez-Pereyra — Resemblance Nominalism: A Solution to the Problem of Universals (2002)
The leading modern defense of resemblance nominalism.
Links: https://global.oup.com/academic/product/resemblance-nominalism-9780199243778 (Oxford University Press) • NDPR review: https://ndpr.nd.edu/reviews/resemblance-nominalism-a-solution-to-the-problem-of-universals/ (Notre Dame Philosophical Reviews)
Douglas Ehring — Tropes: Properties, Objects, and Mental Causation (2011)
A sophisticated trope theory (particularized properties) and applications to mental causation.
Links: PhilPapers entry: https://philpapers.org/rec/EHRTPO-2 (PhilPapers) • Philosophical Quarterly review: https://academic.oup.com/pq/article-abstract/63/251/379/1539440 (OUP Academic)
Anna-Sofia Maurin — If Tropes (2002)
Rigorous, one-category trope ontology; widely cited.
Links: PhilPapers: https://philpapers.org/rec/MAUIT (PhilPapers) • Publisher listing: https://www.abebooks.com/Tropes-MAURIN-Anna-Sofia-Kluwer-Academic-Publishers/14174467293/bd(AbeBooks)

Samuel Newlands (ed.) — The Problem of Universals in Early Modern Philosophy (2018)
How early moderns (e.g., Spinoza, Leibniz) reworked the medieval debate that underpins conceptualism and realism/nominalism.
Links: NDPR review: https://ndpr.nd.edu/reviews/the-problem-of-universals-in-early-modern-philosophy/ (Notre Dame Philosophical Reviews) • Amazon: https://www.amazon.com/Problem-Universals-Early-Modern-Philosophy/dp/0190608048 (Amazon)

Michael J. Loux (ed.) — Universals and Particulars: Readings in Ontology (1970)
Classic reader collecting landmark papers on universals, particulars, individuation.
Links: Internet Archive record: https://archive.org/details/universalspartic00loux (Internet Archive) • PhilPapers: https://philpapers.org/rec/LOUUAP (PhilPapers)
D. H. Mellor & Alex Oliver (eds.) — Properties (Oxford Readings in Philosophy, 1997)
A superb modern anthology on properties/kinds with several essentials for the universals debate.
Links: OUP page: https://global.oup.com/academic/product/properties-9780198751762 (Oxford University Press) • PhilPapers: https://philpapers.org/rec/MELP-2 (PhilPapers)

J. P. Moreland — Universals (Central Problems of Philosophy, 2001)
Concise taxonomy of realist, conceptualist, and nominalist options; good for quick orientation and teaching.
Links: Routledge page: https://www.routledge.com/Universals/PorterMoreland/p/book/9781902683232(Routledge) • ThriftBooks: https://www.thriftbooks.com/w/universals-central-problems-of-philosophy-montreal-quebec_jp-moreland_moreland/1411508/ (ThriftBooks)

Stanford Encyclopedia of Philosophy — “The Medieval Problem of Universals”
Excellent background on realist/nominalist/conceptualist moves and their logical setting.
Link: https://plato.stanford.edu/entries/universals-medieval/ (Stanford Encyclopedia of Philosophy)
Internet Encyclopedia of Philosophy — “Universals”
Clear, structured overview of the main positions with pros/cons.
Link: https://iep.utm.edu/universa/ (Internet Encyclopedia of Philosophy)

If you want one book now: read Loux’s Metaphysics chapter, then Armstrong’s short Universals: An Opinionated Introduction.
To compare live options: pair Armstrong (realism) with Rodriguez-Pereyra (resemblance nominalism) and Ehring/Maurin (tropes).
For seminar/course building: use Loux (ed.) and Mellor & Oliver as backbone anthologies, then assign specialist monographs above.