What are the main differences between a commercial head shot and a theatrical headshot? What do agencies look for in each? Also, do actors need a comp card or more pictures showing your whole body in different looks? I had a comp card when I was a young teen but someone told me you only have a comp card if you're planning on doing modeling.
thanks!

Here's a quick reference article I wrote on my blog a year ago, giving examples of the differences between the two:

http://www.justingillphoto.com...ercial-vs-theatrical


And yes, comp cards are pretty much for modeling only.

No comp cards. Even on print auditions, I just use my best headshot.

Justin has given a good explanation on what generally constitutes a commercial and theatrical headshot.

But bear in mind, just because you're smiling and wearing brighter colors does NOT mean that you can't use them for theatrical and vice versa. Your "commercial" headshots can be used for comedy. My commercial agent has gotten me auditions with my more serious "theatrical" headshots. So crossing over can happen.

Agreed with all the above ...

Here's my take on the difference: Guide to Getting a Great Headshot (Part 1: What is a Heashot?)