Abstract: Based on the nearly 25 years in industry, participating on development of large scale complex software systems at Nokia, I will share my journey in understanding what are complex software systems and what are complicated software systems. I'll provide set of definitions to describe difference between the two. Based on the experience and current state of art of complex software systems I'll suggest why we need to distinguish between complex and complicated software systems. The talk is introduction to the research area I would like to explore and I'm aiming at finding possibilities of cooperation within Lasaris lab where topic of complex software systems could be further explored.