Donald Trump's expected to enter a not-guilty plea during his court appearance in New York later.
It's the first time ever that a former US President has faced criminal charges.
It's understood the allegations are linked to payments to a porn star, made during the 2016 election.
The former President has called it a "witch-hunt" and denies any wrongdoing.
Security has been stepped up in New York City over concerns supporters of Mr Trump will hold demonstrations.
New York City mayor Eric Adams, is warning protestors to show restraint.
"Our message is clear and simple. Control yourselves.
"New York City is our home, not a playground For your misplaced anger."
Lawyer Julie Rendelman, says this could just be the beginning of a series of cases.
"Some believe that this case is going to open the floodgates for them to come forward, and if their cases are stronger, this case will almost disappear and the other cases will take more precedent.".
The judge in today's case has ruled that digital devices will not be allowed courtroom when Donald Trump appears later.
His legal team says it made the request to avoid a "circus-like atmosphere."
