Homogeneous olefin oligomerization plays a pivotal role in the field of petrochemistry. Through catalyst, technology, and process developments, market requirements in terms of productivity, selectivity and sustainability have been addressed. Over more than 50 years, intensive research has been devoted to the design of new Group 4 to Group 10 transition metal complexes and to the study of their reactivity towards olefins leading to several breakthroughs of prime importance for academia as well as for industry. Since the early 1960s, IFPEN contributed to bring innovative industrial solutions to different targets from gasoline production to alpha-olefin on purpose processes with over 100 production units built worldwide. Based on nickel, titanium, zirconium or chromium, the catalytic systems for such processes and their next generation are subject to continuous research where the adaptation of the ligand architecture to the nature of the metal and their mode of activation, play a crucial role to control the reaction selectivity and the catalyst lifetime. Interesting relationships between the complex structure and their reactivity have been drawn and will be discussed in selected examples.