Forty years ago this month–Nov. 6, 1978–President Jimmy Carter signed legislation that created America’s first federal historic tax credit (HTC), a 10 percent investment tax credit for commercial buildings that were at least 20 years old and retained at least 75 percent of their existing walls.

In four subsequent decades, the tax credit has been expanded and contracted, but always has served to preserve historic buildings and spur economic activity. In fact, more than $140 billion in private funds have been leveraged by the HTC, resulting in more than 40,000 projects being certified and more than 500,000 housing units built or rehabilitated through the credit.

As the federal HTC marks 40 years as part of the federal tax code, here is a look at key dates over the years, as well as facts and figures that highlight its success.

Click to Enlarge

Click to Enlarge