The financial markets have become more and more important in modern society. The behavior of the financial markets, and its impacts on our society, relies crucially on the behavior of market participants, aka the investors of different types. Although descriptions of the financial markets on the macro level have caught great attentions of investors, regulators, and the ordinary people, how the market participants interact with each other in the financial market may provide deeper insights on how and why the financial markets behave. This book tries to supply as much research on the micro level of financial market behavior as possible to the readers. The author has been doing financial research, especially on the micro level, during the past two decades. The academic research on this broad area has undergone a rapid growth, with new results, methods, theories, and even paradigms, emerging and burgeoning almost every year. As a financial researcher in one of China's top universities, the author has kept monitoring, digesting, and synthesizing the research articles in the area. This book is the outcome of this decades-long routine research work of the author. The book covers the fundamental economic theories of how different investors receive and interpret information. The empirical results of investors behavior are also discussed in depth. The book also shows the basic academic techniques of modeling the investors behavior.