How to tell if a Journal is peer reviewed and/or legitimate? I am working through my dissertation and was just wondering, how would you know if a journal is peer reviewed or actually legitimate? If a journal etc has an ISSN number on them, does this mean the journal is peer reviewed and good to use?
ISSN numbers are cheap and don't mean anything.

There's no algorithmic way to tell if a journal is legitimate, but some indications:


If it's not open access, chances are it's legitimate. Non-OA journals actually have to publish good articles or nobody will subscribe. OA journals can get away with publishing junk since the author pays for it.
Check their website. It's likely to say if the journal is peer-reviewed.
Who's on the editorial board? Are they established researchers in the field the journal covers? 
Who has published in the journal? Are they established researchers in the field the journal covers? Are the articles of poor quality?


If you're unwilling to do the research yourself, you can also check out Cabell's International which maintains whitelists and blacklists (this, however, is not a free service).