I have two websites. Content is related but not duplicated.
If I cross link these two sites back and fourth is there a possibility that either will be penalized for cross linking?
As I understand it, the key word regarding cross linking is "excessive" cross linking. But what would the engines consider "excessive".

I wouldn't worry about linking each site to the other, let's say from the home page, but I wouldn't do it from several pages.

Henrie you're right that excessive is the key. You should be fine putting a few (2 or 3) links here and there back and forth though I would keep it limited. And make sure the links make sense where you put them. Your links should really be there because they provide a value to your site's visiitors. Think about your visitors first and search engines second.

Originally Posted by Henrie

I have two websites. Content is related but not duplicated.
If I cross link these two sites back and fourth is there a possibility that either will be penalized for cross linking?
As I understand it, the key word regarding cross linking is "excessive" cross linking. But what would the engines consider "excessive".

Just make sure the two sites are on seperate ips or it will not help you.

Originally Posted by Visio

Just make sure the two sites are on seperate ips or it will not help you.

It will make no difference at all what IPs they are on.

Most things that the SEO "experts" say will get you banned are perfectly ok to use for the appropriate purpose. Anything and everything when used in an attempt to fool the search engines could get you a penalty.

Cross linking where appropriate, even between your own sites is perfectly ok provided there are plenty of other links to the sites. When your cross linked sites become an "island" (only linked to and from each other) is when the problems will start.

Originally Posted by chrishirst

It will make no difference at all what IPs they are on.

Most things that the SEO "experts" say will get you banned are perfectly ok to use for the appropriate purpose. Anything and everything when used in an attempt to fool the search engines could get you a penalty.

Cross linking where appropriate, even between your own sites is perfectly ok provided there are plenty of other links to the sites. When your cross linked sites become an "island" (only linked to and from each other) is when the problems will start.

I never said it would get you banned. Yet being hosted on the same ip makes it mroe likely that they are owned by the same person. two sites hosted on different ips linking to each other will get better rankings then two sites on the same ip.

Nope being hosted on the same IP does not make it more likely they are owned by the same person.
Yes it's possible, but 100 sites on 100 consecutive IPs could also be owned by the same person in the same datacentre on the same ISP block.

This idea is that needing multiple IPs to cross link is just paranoid fantasy. And it's just plain BS that linked sites on different IP will get better rankings. I am always amazed how ridiculous, non-sensical ideas like this can get believed.
I do realise that people in general like things packaged up neatly into packages, "do this and this will be the result" kind of things, but please do apply a bit of common sense to these ideas. SEO isn't about exact formulas at all.
The SEs aren't some all seeing, all powerful entities waiting to punish you when you stray from the exact path to enlightenment. You will get penalised/banned after blatently trying to fool the algos. If you don't do that, you can do exactly what you want with your site.
It's YOUR site nobody can tell you how to design it and promote it