Filters

I want to get into astrophotograghy in the future but for now I am just doing the homework. I plan on getting a few of the books mentioned here. At the moment I have been reading a lot of internet items about it and I don't see alot of people talking about broadband filters. I see them advertized for astrophoto's but I can't seem to find anything about them in use. can someone direct me to some reading on this subject. Thanks