Modern Portfolio Optimization
Modern portfolio theory (MPT) is also called mean-variance portfolio theory. It is a major cornerstone of financial theory was awarded in 1990 based on this theoretical breakthrough. It was formulated in the 1950s. It is still a finance theory be using in practice today.
Financial Theory and Corporate Policy by Weston, Shastri, Copeland (2013) provides a good introduction to the formal topics associated with MPT.
It is important to notice that the assumption of normal distribution of the stock returns is the foundation of MPT theory.