After the success of the previous editions, we are very glad to announce the WCCS19, “4th Edition of World conference on Complex Systems “. The WCCS19 will be organized by “Moroccan Society of Complex Systems”, “Ibn Zohr University” and National College of IT (ENSIAS, Mohamed V Souissi University) in partnership with IEEE Moroccan section and “International Academy for Systems and Cybernetic Science” during April 22-25, 2019 in Ouarzazate-Morocco. The WCCS19 will provide a high-level international forum for researchers and Ph. D. students who will present recent research results, address new challenges and discuss trends in the area of complex systems and interdisciplinary science. The aims of the conference are focused on the debate about the most relevant methodologies and approaches to understanding, modelling, simulating, predicting, evaluating and mastering the Societal, Ecological, Biological and Engineered Complex Systems.