Energetic particles are a fundamental ingredient of the dynamical Sun. A major part of the energy released during eruptive events in the solar atmosphere is transferred to particles, and then carried into the heliosphere. Transient processes on the solar surface and in the solar atmosphere are capable of energizing electrons (up to tens of MeV) and ions (up to a few GeV) that could escape to the interplanetary space along open magnetic field lines. These particles, ranging from suprathermal (few keV) to relativistic energies, can be observed in-situ as SEP events by radiation detectors in space. Solar flares and Coronal Mass Ejections (CMEs) are the main sources of SEPs. SEP events are also of great relevance for Space Weather because they can cause large radiation increases in interplanetary space and over the Earth’s polar regions, potentially harmful for human crews in space and for space-based technology