This strategic network aims to promote the coordination of initiatives and the participation of Spanish scientific groups in forefront research in Particle, Astroparticle and Nuclear Physics. Research in these areas is carried out in an environment of close international collaboration, usually in large world-class facilities and laboratories and with the participation of a large number of people and institutions. This inevitably implies long- term commitments, both in terms of funding and human resources, which must be carefully analyzed and eventually coordinated. Therefore, it is necessary to establish a well-defined scientific strategy, at the national level, with long-term objectives.
A large part of the scientific activity is associated with CERN, the most important European Research Infrastructure, where Spanish groups participate in cutting-edge international experiments and have a significant fraction of their personnel working there. In nuclear physics we also participate in other important European research infrastructures, such as the future "Antiprotons and Heavy Ions Factory" (FAIR) in GSI or the heavy ion accelerator GANIL and its recent upgrade SPIRAL2. The Spanish astroparticle community is currently leading the ambitious project to build a "Cherenkov Telescope Network" (CTA-North) on the island of La Palma, and participates in the European project of a large submarine neutrino telescope KM3NeT, as well as in experiments of detection of gravitational waves (LIGO, VIRGO, Einstein Telescope, LISA), cosmology (DES, DESI, PAU...), dark matter and axions, in different laboratories of international character. All these major projects are part of the "ESFRI Roadmap" and are subject to a careful international planning and supervision process: ECFA, ESPP, NuPECC, ApPEC. It is essential to encourage the Spanish participation in the definition of these European strategies.