  In his Nobel Prize lecture Victor Hess urged that different instruments,
working together, should be used to solve the problem of the origin of cosmic
rays. I review some of the key developments that have opened up the new fields
of direct and indirect multi-messenger astronomy and that are guiding us to the
solution of this riddle. I then discuss, very briefly, some of the new
instruments that are shortly to come on line and give examples to show the long
lead-times from conception to implementation that occur in this field. I
conclude with some remarks about very ambitious future projects. The paper is
not intended as a review: rather it is an attempt to set down issues discussed
in the Hess Memorial Public Lecture given at the 2019 ICRC in Madison,
Wisconsin and accessible at www.icrc2019.org.
