Abstract: In this paper, a novel algorithm, combining trust region and particle filtering, is proposed for target tracking in FLIR imagery. Trust regions and particle filters are two successful methods for object tracking. Both of them have their respective advantages and disadvantages. The proposed algorithm integrates the advantages of the two approaches. Compared with the original particle filters and trust regions, this new algorithm can maintain multiple hypotheses with fewer particles by encouraging the particles to be in the right part of the state space. Thus, the sample degeneracy problem and sample impoverishment problem could be overcome. The experiments performed on several infrared sequences show the robustness of the proposed algorithm.