Encyclopedias, Almanacs, Transcripts, and Maps
- Aretes
- Argelia Velez-Rodriguez
- Argentum, Potabile
- Arginase deficiency
- Arginase Deficiency
- Arignote
- Arigó, José (1918-1971)
- Ariolists
- Aristaeus the Elder
- Aristotelian Physics, Impetus Theory, and the Mean Speed Theorem
- Aristotle and Aristotelianism
- Arithmancy
- Armadillos: Dasypodidae
- Armand Hippolyte Louis Fizeau
- Armand James Quick
- Armand Séguin
- Armida
- Armillaria ostoyae
- Armomancy
- Arnau de Villanova