All Answers

For the most part, you don't put the dress code on the invitations unless it is black-tie because your guests are supposed to infer the dress code from the time of day, so if you want to include it, it is up to you. You could simply include the line "Semi-Formal Attire Please" at the very bottom of your invitations. But, if your motivation for doing this is to avoid having some underdressed or inappropriately dressed folks at your wedding, please realize that they are going to be there regardless of what you put on your invitations. Some people have no concept of what appropriate dress is, not matter what you put on your invites. Don't stress out about them "ruining" your day with their bad outfits, you'll be so swept up in the moment that you won't notice and you can ask your photographer to keep them out of pictures or stash them in the back...

I usually write this at the bottom of the invitation off center (i.e. to the right or left) ex. Black Tie Affair, Evening Wear, Cocktail Wear, etc. I'd be glad to help with wording and/or your whole invitation package. Good luck. P.S. If you know who is going to show up in the leisure suit, have someone else in the family bring it up in a conversation like, "I can't wait to wear my new Vera Wang (or whatever) dress to the Bolden wedding. It's going to be so elegant and formal. What will you be wearing?" Something like that.

At the bottom of your invite (or somewhere on there) list exactly that... "Semi Formal Attire Required" or "Formal Attire Please" whatever you fancy. Some reception places (I went to a wedding like this one time) won't even let you get a drink (if you are male) without your suite coat on... everytime they wanted a drink they had to put it back on... So make sure you find out what the dress code (if there is one) at your reception venue is before you make that decision. I am having a semi formal event and you can bet that will be somewhere on my invites!!! :)
Also... both you and your guest will feel awkward if they dont know what to wear and show up in something thats not dressy at all or something that is way too dressy... so listing it is only helpful to both parties involved.

You have some really good answers here, but in a very real way, Mr. Bolden3's answer is the best. By that, I mean that what is important is that you are sharing your great joy with your friends and family, and they are there to express their love and support for you both by being there.

No matter what you put on the invitation... no matter what you say to people in conversation... there will still be a few who think khakis and a golf shirt means "semi-formal."

No matter how elegant the reception, some just won't "get it."

The key is to be gracious to those who do not comply with your wishes. Mentally mutter for a moment and then smile and say, "It's so NICE you could share our special day with us. Thank you for coming!" Then immediately forget about it and have fun!

Best wishes to both of you!

I didnt put a dress code on my invite, but I did spread the word to people in the family that I would most likely show up in jeans!

The look and style of your invitations will determine the formality of your event. They will set the tone for what kind of reception you're having. Make sure they correlate to the time and place of your reception. For a semi-formal to formal wedding I would do thermal engraved invitations with hand calligraphy. No matter what you do, you're always going to get one or two guests who don't know how to dress appropriately for a wedding. You'll be so busy with getting married and being a new bride you won't even notice who's wearing what. Enjoy your day!