Advances in Hydrogen Molecular Ions: H3+, H5+ and beyond, a scientific discussion meeting organised by Professor Jonathan Tennyson FRS, Professor Benjamin McCall and Professor Steven Miller, will take place at the Royal Society, London, on 21-22 January 2019. This meeting will highlight recent developments in theoretical, laboratory and astronomical studies of the molecular ion H3+ and its hydrogenated cousin H5+. These developments include the first models of H5+, high-resolution studies of H3+ deuterated isotopologues, ultra-cold chemistry studies, new chemical models of the Galactic Centre, and data from the space missions Cassini (Saturn) and JUNO (Jupiter). Attendance is free, please register on the website. The deadline for submitting poster abstracts is 26 November.