Abstract : This work is devoted to segmentation and tracking of structures undergoing large deformation in an image sequence. The overall goal is the modeling of complex moving and deforming structures that simultaneously brings compression of data, segmentation and tracking on temporal sequences of images. Deforming entities are approximated by implicit templates, defined as level sets of some particular implicit functions. Implicit functions provide interesting tools for the modeling of visco-elastic objects. Structures are approximated using an energy minimization process; the energy functional carries information about position, tangent and curvature. The implicit functions are defined by some control points, their radius of influence, and an iso-value. Once the structures are segmented, tracking is modeled using the displacements of the control points and the variation of the radii of influence. The method is first applied on a sequence of images displaying a vortex formation, and the authors show that such a vortex structure can be segmented and tracked with implicit functions.