  Citation: Hernández-Rey, J.J.; Ardid, M.; Bou Cabo, M.; Calvo, D.; Díaz, A.F.; Gozzini, S.R.; Martínez-Mora, J.A.; Navas, S.; Real, D.; Calvo, D.; et al. Science with Neutrino Telescopes in Spain. Universe 2022, 8, 89. https://doi.org/10.3390/ universe8020089 Academic Editors: Susana Cebrian Guajardo, María Martínez Pérez and Carlos Peña Garay Received: 15 December 2021 Accepted: 6 January 2022 Published: 29 January 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). universe Article Science with Neutrino Telescopes in Spain Juan José Hernández-Rey 1, * , Miguel Ardid 2 , Manuel Bou Cabo 3 , David Calvo 1 , Antonio F. Díaz 4 , Sara Rebecca Gozzini 1 , Juan A. Martínez-Mora 2 , Sergio Navas 5 , Diego Real 1 , Francisco Salesa Greus 1, * , Agustín Sánchez Losa 1 , Juan de Dios Zornoza 1 and Juan Zúñiga 1 1 IFIC—Instituto de Física Corpuscular, Universitat de València and CSIC , C/Catedrático José Beltrán, 2, 46980 Paterna, Spain; dacaldia@ific.uv.es (D.C.); sara.gozzini@ific.uv.es (S.R.G.); real@ific.uv.es (D.R.); Agustin.Sanchez@ific.uv.es (A.S.L.); zornoza@ific.uv.es (J.d.D.Z.); Juan.Zuniga@ific.uv.es (J.Z.) 2 Instituto de Investigación para la Gestión Integrada de las Zonas Costeras, Universitat Politècnica de València, C/ Paranimf, 1, 46730 Gandia, Spain; mardid@fis.upv.es (M.A.); jmmora@fis.upv.es (J.A.M.-M.) 3 Instituto Español de Oceanografía, Unidad Mixta IEO-UPV, C/Paranimf, 1, 46730 Gandia, Spain; manuel.bou@ieo.es 4 Department of Computer Architecture and Technology/CITIC, University of Granada, 18071 Granada, Spain; afdiaz@ugr.es 5 Departamento de Física Teórica y del Cosmos and C.A.F.P.E., University of Granada, 18071 Granada, Spain; navas@ugr.es * Correspondence: Juan.J.Hernandez@ific.uv.es (J.J.H.-R.); sagreus@ific.uv.es (F.S.G.) Abstract: The primary scientific goal of neutrino telescopes is the detection and study of cosmic neutrino signals. However, the range of physics topics that these instruments can tackle is exceedingly wide and diverse. Neutrinos coming from outside the Earth, in association with other messengers, can contribute to clarify the question of the mechanisms that power the astrophysical accelerators which are known to exist from the observation of high-energy cosmic and gamma rays. Cosmic neutrinos can also be used to bring relevant information about the nature of dark matter, to study the intrinsic properties of neutrinos and to look for physics beyond the Standard Model. Likewise, atmospheric neutrinos can be used to study an ample variety of particle physics issues, such as neutrino oscillation phenomena, the determination of the neutrino mass ordering, non-standard neutrino interactions, neutrino decays and a diversity of other physics topics. In this article, we review a selected number of these topics, chosen on the basis of their scientific relevance and the involvement in their study of the Spanish physics community working in the KM3NeT and ANTARES neutrino telescopes. Keywords: neutrino; neutrino telescopes; neutrino astrophysics; neutrino properties; sea science 1. Introduction During the last decade, neutrino astronomy has enjoyed a true revolution following the detection of the first signals of very high-energy neutrinos [1] by the IceCube detector [2]. It has been a long way since the key concepts were proposed by M. Markov in 1961 [3]. Arriving at this point has required an enormous experimental effort and the determination and perseverance of hundreds of physicists and engineers. The potential to expand the harvest of scientific results in a variety of areas makes this endeavour worth pursuing. Several Spanish research groups have participated in the past and continue to participate at present in this worldwide undertaking through their work in the ANTARES [4] and KM3NeT [5] neutrino telescopes. In this article we review the contributions of the Spanish groups to these projects in the areas of design, construction, calibration, operation and physics analyses. Neutrino telescopes have a very wide scientific scope. The rationale of these detectors stems from the fact that neutrinos are, at the same time, neutral, weakly-interacting particles and also the final, stable product of a variety of nuclear and particle physics processes. Universe 2022, 8, 89. https://doi.org/10.3390/universe8020089 https://www.mdpi.com/journal/universe