This volume contains the proceedings of the third Euroconference on Atomic Phys ics at Accelerators (APAC 2001), with the title Stored Particles and Fundamental Physics. It was held in Aarhus, Denmark, from September 8 to 13 at the Marselis Hotel located near the beach and the Marselis Woods outside Aarhus, but some of the activities took place at the Department of Physics, University of Aarhus. The conference was sponsored by the Commission of the European Union (Contract No. ERBFMMACT980469) and also by the Danish Research Foundation through ACAP (Aarhus Center for Atomic Physics). The meeting was focused on the application of storage rings for atomic physics, and there are two fairly small rings in Aarhus, ASTRID (Aarhus STorage Ring for Ions,Denmark) and ELISA (ELectrostatic Ion Storage ring, Aarhus). The research at these rings has contributed to the strong position of European Science in this field. Both rings are designed according to unique concepts. ASTRID is a dual purpose ring, which half the time stores electrons for the generation of low-energy synchrotron radiation. The storage of negative particles has also been a unique feature for the application of ASTRID as an ion storage ring.