Theme Issues:

1. W. Just, A. Pelster, M. Schanz, and E. Schöll (Editors):
   Delayed Complex Systems;
   Philosophical Transactions of the Royal Society A 368, 303-513 (2010)

2. A. Hutt, A. Pelster, C. Uhl, and J. Kurths (Editors):
   In memoriam Hermann Haken: synergetics and self-organiation in complex systems;
   The European Physical Journal Special Topics 235 (2026)