(UK) Nottingham University - Number Theory and Arithmetic Geometry research group. Research interests, members, visitors, meetings. (USA) University of Texas - Number Theory Group. Members, meetings, software. (Israel) Ben Gurion University of the Negev - Number Theory and Algebraic Geometry Research Group. Members, research interest, seminars. (USA) University of South Carolina - Number Theory Group. Members, research interests, courses, links. (USA) Boston University - Algebra and Number Theory Research Group. Members, research interests, seminars, courses. (Netherlands) University of Leiden - Number theory research group. Staff, events, links. (Hungary) Alfréd Rényi Institute of Mathematics, Hungarian Academy of Sciences - Number Theory research group staff. (UK) University of York - Number Theory Research Group. (USA) University of California, Santa Barbara - Arithmetic and Geometry Seminar. Meetings. (Croatia) University of Zagreb - Seminar on Number Theory and Algebra. Members, seminars, links. (UK) University of Cambridge - Number Theory Seminar. Meetings. (Canada) University of British Columbia - Number Theory group. Members, research areas and meetings. (Italy) University of Pisa - Number Theory Group. Research interests and members. (China) Shandong University - Number theory research group. Members, research interests, courses, events. (USA) Southwestern Center for Arithmetical Algebraic Geometry - Based at the University of Arizona, in collaboration with the Universities of New Mexico, Southern California, and Texas. Annual conference. (Hungary) Lajos Kossuth University, Debrecen - Department of Algebra and Number Theory. Staff list. (Europe) Arithmetic Algebraic Geometry - A European network of 12 working groups from 6 countries. (UK) University of Glasgow - Number Theory and Combinatorics. Staff, research interests. (USA) University of Rochester - Algebra and Number Theory Group. Members, research interests, seminar schedule. (Germany) University of Regensburg/Leipzig - Algebraic Cycles and L-Functions research group. People, preprints, seminars, workshops, positions, news. (Canada) Queen's University, Kingston - Algebra and Number Theory Group. Members, research interests. (USA) University of Illinois at Urbana-Champaign - Number Theory faculty, visitors, meetings, courses, events. (UK) University of Oxford - Number Theory Group. Members, publications, meetings. Number Theory Centres - Listed in the Number Theory Web. (USA) Brown University - Number Theory/Arithmetic Geometry Seminar. Members, meetings. (UK) University of Bristol - Number Theory group. Staff, students, events, links. (UK) King's College London - Number Theory Group. Staff, meetings, preprints. (Canada) CICMA, Concordia University, Montreal - Research in number theory and arithmetic geometry. Members, seminars, preprints. (Hungary) Eötvös University, Budapest - Department of Algebra and Number Theory. Events, publications, members' pages. (UK) Cardiff University - Number Theory Group. Members, research interests, advice to research students. (UK) University of Durham - Geometry and Arithmetic Group. Members, meetings, preprints. (UK) Royal Holloway, University of London - Research areas (mainly analytic/combinatorial), members. (USA)University of Michigan - Graduate Program in Number Theory. Staff, research interests, courses, seminars.