REITs started to exist in the 1960s and were introduced in the United States with the law 86-779, which allowed individuals to invest in large, diversified portfolios of income-producing properties.
Following, in 1986, a new Tax reform came into place that helped to accelerate the growth of REITs. From now on, the same entity was allowed to manage and own the real estate.
As of today, 40 countries have adopted the principle and in the US alone, the market capitalization has reached $1.35 trillion.