Odgers, Ben
- University of Bristol. Prime numbers, the Riemann zeta function, L-functions, and random matrix theory.
- http://www.maths.bris.ac.uk/~mabeo/

Oyono, Roger
- Universität Duisburg-Essen. Arithmetic on Jacobians. Publications, thesis.
- http://www.exp-math.uni-essen.de/~oyono/

Ochiai, Tadashi
- Osaka University. Number theory, arithmetic geometry. Papers, preprints.
- http://www.math.wani.osaka-u.ac.jp/group/ochiai/index-e.html

Ouyang, Yi
- University of Toronto. Algebraic number theory and arithmetic geometry: cohomological tools to study the arithmetic properties of number fields. Publications.
- http://www.math.toronto.edu/youyang/

Okazaki, Ryotaro
- Doshisha University. Unit Equation; Class Field Theory of CM-fields; Continued Fractions. Papers, teaching materials.
- http://www1.doshisha.ac.jp/~rokazaki/

Oort, Frans
- University of Utrecht. Algebraic geometry and number theory. Publications, links.
- http://www.math.ruu.nl/people/oort/

Ono, Ken
- University of Wisconsin. Combinatorics and Number Theory involving Elliptic curves, L-functions, modular forms and partitions. Publications, activities, resources.
- http://www.math.wisc.edu/~ono/

Omar, Sami
- University of Essen. Zeroes of L-functions and related topics; Cryptography; Computational number theory; Random Matrix theory and L-functions.
- http://www.exp-math.uni-essen.de/~omar/

O'Neil, Catherine
- M.I.T. Number theory, Arithmetic algebraic geometry.
- http://www-math.mit.edu/~coneil/