Powerful relativistic outflows are associated to the brightest sources in the sky. These sources reach their large luminosities at very high energies through non-thermal emission. The relativistic particles responsible of this non-thermal emission are the result of different acceleration mechanisms, which can take place in different regions linked to these outflows. The production of relativistic particles is very sensitive to the local conditions, and therefore their radiation probes the physical properties of the plasmas in which they are generated. Several objects are perfect places to study the physics of relativistic outflows: pulsars, microquasars, and active galactic nuclei (AGN). Depending on the source, these outflows can be either collimated (jets) or wide (winds). Nowadays, the main unknowns of jets and winds concern their formation mechanism, the way how they propagate and dissipate energy, the role of the environment to trigger emission and mass-loading, and the way how they terminate and the global impact on the medium. We aim at answering, studying the high energy emission from relativistic outflows, the following questions: the content and structure of jets in microquasars and AGN at their formation region; the propagation of these jets; the impact of pulsars on their environment in binary systems at all scales; the radiative and dynamical consequences of these outflows when terminating. Different techniques will be used to achieve our goals: semi-analytical modeling; numerical (magneto)hydrodynamical simulations; numerical calculations of radiation transfer; and multiwavelength observations.