We are pleased to announce the 15th workshop on breakdown science and high gradient technology, HG2023, that will be held in person in Italy at the Frascati National Labs of INFN – Via Enrico Fermi, 60 – Frascati (Rome) from 16 to 20 October 2023.The demand for pushing the RF structures operation to higher and higher accelerating gradients has been historically driven by the High Energy Physics community need of expanding the energy frontier of the discovery machines. This demand is still far to be exhausted, as clearly stated in the Accelerator R&D Roadmap for the European HEP Strategy released in late 2021. But high gradients are also extremely beneficial for accelerators destinated to different fields, such as compact light sources, medical and industrial applications, that are growing more and more as new drivers of the HG technology.The HG workshop covers revisitations of basics and fundamentals concepts, recent theoretical and experimental achievements, advancements in modelling and understanding of the breakdown phenomena, new design concepts and innovation in manufacturing techniques, ideas and experimental activities towards more powerful and efficient RF power sources, reports on the existing test benches and plans for new ones, and much more! It is a unique opportunity to sketch a comprehensive landscape of a truly global activity, with many pulsing research sites spread all over the continents.And, finally, it is the first opportunity to gather our community face to face since 2019, after the pandemic hard times. For all these reasons we look forward to seeing you at Frascati HG2023!Due to the ongoing conflict in Ukraine, the HG2023 meeting is unable to accept any registrations from any organisation based in Russia or Belarus.Participants in the Workshop are invited to register via web using the online registration form (handled via an INFN indico page – an INFN indico account required). The registration fee of 500,00 Euros (tax included), as contribution to the Workshop organisation, includes lunches, coffee breaks, cheese and wine during the poster sessions, a welcome cocktail, a social dinner + bus to/from the restaurant and meeting materials.For the participation on site it is mandatory to be registered to the event and to show the badge.Industrial exhibitors are invited to register via web through the registration form. The registration fee of 1000,00 Euros (tax included) includes a dedicated space in the foyer venue of Bldg. 36 and one representative registration fee, the logo on the workshop website linked to the commercial page on display and in the conference folder.Students can apply for a student grant. Please follow all the instructions on the dedicated web page.Those who need to apply for a VISA to enter Italy are kindly requested to ask for a formal invitation letter by e-mail to the Workshop Secretariat.CANCELLATION AND REFUNDSAll refund requests must be in writing by mail to the Workshop Organisers as soon as possibleRegistration fee less 50,00 € as administrative fee, will be refunded if a request is made in writing to the HG 2023 Secretariat (hg2023@lists.lnf.infn.it) and received prior August 31st, 2023. Cancellations after this date will be non-refundable, also for “STORNI INFN” and no show.Registrations may be transferred to substitute delegates without incurring a fine. Local Organising Committee:    Alesini D. (INFN-LNF, Italy)Bilanishvili S. (INFN-LNF, Italy)Cardelli F. (INFN-LNF, Italy)Carillo M. (INFN-LNF, Italy)Faillace L. (INFN-LNF, Italy)Ferrazza M.R. Coordinator (INFN-LNF, Italy)Gallo A. Chair (INFN-LNF, Italy)Giabbai M. Coordinator (INFN-LNF, Italy)   Piersanti L. (INFN-LNF, Italy)Tocci S. (INFN-LNF, Italy)