The United States fifty-dollar bill is currently in circulation and remains a legal tender. The current design of the fifty-dollar bill was introduced in 2017 and features a portrait of Ulysses S. Grant, the 18th president of the United States, on the front.

However, there have been previous versions of the fifty-dollar bill that are no longer in circulation. The first version of the fifty-dollar bill was introduced in 1913 and featured a portrait of William McKinley, the 25th president of the United States, on the front. This version of the bill remained in circulation until 1928 when a new design was introduced featuring a portrait of Ulysses S. Grant.
The design of the fifty-dollar bill continued to evolve over the years with various changes to the portrait and security features. In 1996, a new design was introduced featuring a portrait of Ulysses S. Grant on the front and a vignette of the U.S. Capitol building on the back. This design remained in circulation until 2004 when a new design was introduced featuring a portrait of Ulysses S. Grant on the front and a vignette of the U.S. Capitol building on the back with additional security features.
In 2013, the United States Treasury announced that it would be redesigning the fifty-dollar bill to include additional security features to combat counterfeiting. The new design was introduced in 2017 and features a portrait of Ulysses S. Grant on the front and a vignette of the U.S. Capitol building on the back. The new design also includes a security thread that glows blue under ultraviolet light and a watermark of Ulysses S. Grant that is visible when held up to the light.
While the design of the fifty-dollar bill has changed over time, it remains a legal tender and can be used for transactions in the United States. The United States Treasury continues to monitor the circulation of all denominations of U.S. currency to ensure that they remain secure and free from counterfeiting.
In conclusion, the fifty-dollar bill is still in circulation in the United States, and there have been previous versions of the bill that are no longer in circulation. The current design of the fifty-dollar bill was introduced in 2017 and features a portrait of Ulysses S. Grant on the front with additional security features to combat counterfeiting.