No. 61 (00178) Family name : Hernando Given name : Jose Angel Affiliation : CERN and University of Santiago, Spain Abbreviation : E-mail address : jose.hernando@cern.ch Title : "RecPack": An Object Oriented code to fit dynamic trajectories. Authors : A Cervera, J.J. Gomez-Cadenas, JA Hernando Abstract : We have implemented a general tracking object oriented code, called "RecPack", to reconstruct dynamic trajectories in any experimental setup. The basic utility of the package is the fitting of trajectories in the presence of random noise processes (multiple scattering, etc) via a Kalman Filter. The package also includes an analytical navigator to extrapolate trajectories to any surface, path length computations, matching functions (trajectory-trajectory, trajectory-measurement) and more.