Star Wars: Heir to the Empire is part one in a three-book cycle. It is also referred to as “The Thrawn Trilogy”. (Thrawn is a main character in the trilogy). All three books were written by Timothy Zahn.
There seems to be some debate over whether or not The Thrawn Trilogy is considered to be canon in Star Wars lore. Some say it is (or that it should be). Others point out that the upcoming Star Wars movies aren’t following closely to what happens in this trilogy, or that they may have thrown it out altogether. I haven’t done much digging into that whole debate, so I’ll simply note it here and move on.