The process of filing an appeal in a case is not as straightforward as one might think. WGBH News' Morning Edition Host Joe Mathieu spoke with Northeastern University law professor and WGBH legal analyst Daniel Medwed to talk about how appeals work. The transcript below has been edited for clarity.

Joe Mathieu: What can be appealed to a higher court?

Daniel Medwed: Well, not everything can be appealed. Each jurisdiction has very carefully delineated what may and may not be appealed. So in the criminal context, you can always appeal your final judgment — the conviction and sentence against you — but typically not preliminary decisions, except for certain decisions that affect the prosecution. If the prosecution can't go forward in the case, maybe evidence has been suppressed, they are allowed to file what's called a special interlocutory appeal. But generally speaking, you can't just stop a case midstream and appeal each and every little decision that you're upset about. You have to wait until there's a final decision.

Mathieu: Let's say things don't go your way during trial. Is there a chance for a redo?

Medwed: It's not a chance to do it all over again. Instead, it's an opportunity to have a second set of eyes look at the same issues, and you're really restricted in what you can raise on appeal. For one thing, you may not present any new evidence — no new witnesses [and] no new documents. And to a large extent, you're confined to the issues that you presented down below. There's something called the preservation requirement: you have to present all of the issues at trial [and] have them adjudicated in order for them to be adequately preserved for appellate review. What's more, appeals courts are often very deferential to trial court decisions and the level of deference hinges on the precise issue that you're raising. So let's say you're contesting a factual finding by a trial judge. The trial judge has decided that it was raining on the night of a fatal car accident. If you want to challenge that, it's very difficult because there's a presumption of correctness that attaches to that finding. Likewise, if the judge has made some type of discretionary decision to exclude or admit evidence, you have to show that she abused her discretion in order for it to be reversed. So there are [a lot] of limitations on what you can do on appeal.

Mathieu: Is there a difference in appealing a case on [the federal versus the state] level?

Medwed: Well, not necessarily in terms of the mechanics. But in terms of location, yes. If you have a state case here in Massachusetts and you've lost in the trial court, you have an appeal as a right to our intermediate court. It's called The Massachusetts Appeals Court. If you lose there you can ask — or really beg — for our highest court, the Supreme Judicial Court, to take the case. And if you lose there at the SJC, you can ask the Supreme Court of the United States to take the case. Let's say you lose at the federal district court here in Boston, which is over at the Moakley Courthouse in Southie. If you lose there, you have to appeal to a Federal Circuit Court of Appeals. The one that covers Boston is called the First Circuit. It covers most of the New England states and Puerto Rico. If you lose in the circuit, you then have to ask the U.S. Supreme Court to take your case.

Mathieu: So how do you do that? You hear people say, "I will take this all the way to the Supreme Court." There must be thousands of requests. What are they looking for?

Medwed: [There are] thousands and thousands of requests. And the Supreme Court has been taking about 50 to 60, maybe 80 cases in recent years — very, very few, a needle in a haystack. I think they're looking for one of two things. First, a split in the lower courts. Is there some type of fissure [or] uncertainty, specifically in the federal circuits, that the Supreme Court has to resolve to create some uniformity? Second and sometimes related, is it an issue of pressing national significance? Are people just clamoring for information about it? I'm thinking about things like abortion, same-sex marriage [and] gun control. Those are issues the Supreme Court might take just to send a message about what the law of the land is.