Electromagnetic ion traps have become essential instruments for the precise and accurate mass determination of rare isotopes. Penning trap mass spectrometers are now successfully operated at several radioactive beam facilities in the world. Accurate masses values obtained with these devices provide key data for the test of fundamental interactions, the modeling of the nuclear synthesis of the elements, and for improving our understanding of nuclear structure far from stability. This paper gives an overview of the basic techniques, the specific challenges, and the status of Penning trap mass spectrometry of rare isotopes.

PACS numbers: 21.10.Dr, 34.50.Bw, 41.85.Ja, 29.25.Rm