Talking Tech: Can you play DVDs on a Blu-ray player?

Can you play DVDs on a Blu-ray player?
Yes, you can.
In fact, millions of consumers play DVDs on Blu-ray players every day. I do it at least once a week, maybe more, when I'm watching content that is available on DVD but not on Blu-ray, especially old TV shows or documentaries that were made decades ago and might be too expensive to convert to high definition home media.
Blu-ray discs (BDs) are essentially the “next logical step” in the digital optical disc data storage format known as the Digital Video Disc, which itself was a descendant of the audio compact disc of the early 1980s. It’s no coincidence that CDs, DVDs, and BDs share the same dimensions - 120 millimeters (4.7 in) in diameter and 1.2 millimeters (0.047 in) thick.
The main difference between a DVD and a BD is that the latter can store more information (50 gigabytes worth in a double-layer BD) than a DVD. This is because the disc is read by a blue (actually violet) laser that can read more data than the average DVD player’s red beam.
Of course, the inventors of the Blu-ray format (as well as of its competing high-definition disc, the abandoned HD-DVD) designed the new players to be “downward compatible” with the existing (and popular) DVD discs, which themselves are based on the 1980s-era compact discs.
Thus, consumers who made the transition from older standard definition TVs to the new high-definition sets can have their cake and eat it, too. Unlike, say, the transition from VHS videocassette recorders to DVD players, if you have a sizeable DVD collection and buy a Blu-ray player for your HDTV, you don’t have to throw out your favorite DVDs. A Blu-ray player will play compact discs and DVDs just fine.

A Caveat

This doesn't apply if you are talking about playing a DVD that has a Region X code and you have a Region Y-locked player. 

For instance, if you live in the U.S. (Region 1 or A) and bought a region-locked Blu-ray player, you can't play DVDs with a Region 4 (Europe and UK) code. If the discs have no region coding (they are usually labeled as "region-free") or have a "Region Free" player, obviously the discs will work just fine. But if you have a European-made DVD that's locked with a regional code, forget it.

Oh, and one more thing. While you can play DVDs on a Blu-ray player, you can't play a Blu-ray disc on DVD player. The discs may be first cousins, but the DVD player's red laser beam won't read the data in a BD disc.