Water is the first thing that comes to mind when we think of a liquid, yet it is the one we understand the least.

Liquids are one of the most underdeveloped fields in physics. The reason for this is that solids have an ideal form in crystals, and gases have an ideal gas. Many things can be explained by considering how much they deviate from these ideal states. In contrast, no such ideal state exists for liquids. Because this approach is difficult, the field has been left neglected for many years. When I was a student, Dr. Hideki Yukawa asked, "Won't someone take this on?" and it has been on my mind ever since. Now, the time is ripe. With the development of experimental techniques like X-rays, the advancement of computers that facilitate sophisticated simulations, and growing interest in complex systems, the environment is finally in place to tackle this in earnest. So, I decided to do it. Specifically, I took on the role of leader, organized about 40 physicists from across the country, and for three years, we worked on "complex liquids" as a Grant-in-Aid for Scientific Research on Priority Areas from the Ministry of Education. Complex liquids include things like polymers, which are like tangled snakes, liquid crystals, and water, where electrons are involved and exhibit complexity, as well as those whose complexity derives from environmental conditions, such as supercooling. I take pride in the fact that this is a research theme I created myself, as no systematic approach to this field has been undertaken anywhere else in the world. One of my goals is to first gain a better understanding of water. Water is a substance essential to life, and understanding it is crucial for elucidating life phenomena. I believe that the study of complex liquids will also serve as an important touchstone for future research on complex systems in general.