Can a blu-ray dvd player play normal DVDs as well as blu-ray dvds?

I have a sony DVD player but that wont play most DVDs. So I was going to get a new dvd player. With all the buzz about blu-ray I was thinking of upgrading to a blu-ray DVD player NOT by sony. But i’m wondering if that will play most DVDs.

Related posts:

1. Can you play regular DVDs in a Blu-Ray DVD player?
2. Does the sony BDP S1E blu ray dvd player read normal dvds?
3. can an hd/blu ray dvd play on a regular dvd player and still have the same picture quality?
4. can an hd/blu ray dvd play on a regular dvd player and still have the same picture quality?
5. Can a blu-ray DVD play on an old DVD player or does the DVD player HAVE to be blu-ray compatable?