A space weather service is based primarily on observations. The system to observe is however huge: from the whole Sun to little structures on its surface to local disurbances of the ionosphere, together with large and small scale changes of the magnetosphere. Each physical processes leading to perturbation of the space environment has its own signature, from UV to radio emission. The goal of this talk it to provide an overview of the different observing signatures and instrumetal means necessary to provide the necessary information to a Space Weather Center.