In view of the limitation on length set by the cost of producing the IAU Reports, the present report can only be a selection of the most important advances during the past three years and not a complete review of the field.
Attempting to pick out a few points of interest, since the last report improvements have been made in recording solar X-ray spectra and in high spatial resolution imaging; the OSO satellite programme continues to produce valuable data. The eclipse experiments planned for March 1970 will, if successful, provide a considerable amount of new information. The solar iron abundance is still a subject of interest in view of the revision of oscillator strengths used in the photospheric analyses. Further interplanetary observations have shown that the general nature of the solar wind at the Earth does not depend on the phase of the solar activity cycle, and have revealed large increases in the abundance of helium in the solar wind following solar flares.