Recent experimental confirmation that neutrinos oscillate from one type or 'flavour' into another during their path from the Sun to Earth was the prime topic of discussion at the Sixth School on Non-Accelerator Astroparticle Physics held at ICTP from 9 to 20 July. The confirmation, made in an underground detector at the Sudbury Neutrino Laboratory near Sudbury, Ontario, Canada, provides the most convincing piece of evidence yet for solving the 30-year-old 'missing neutrinos' puzzle, thus confirming our models for the Sun's nuclear reactions. Neutrino oscillations were first hypothesised by Bruno Pontecorvo, who was an original member of Enrico Fermi's famed team of theoretical physicists assembled in Rome during the 1930s. The experimental results strongly favour the Mikheyev-Smirnov-Wolfenstein 'in-matter oscillation' scenario. Alexei Smirnov is a scientist in the ICTP High Energy group.