These envelopes are called Invitation envelopes, but we have used them for cards, thankyou notes, and other similar things. The envelopes come in a box of 10. They are available only in White and Ivory, which is fine for business purposes, but for party invitations and such we would probably like more color options. I like these envelopes' quality look and feel and the fact that they are easy to seal with their self-seal flap. They hold a standard size card and regular business size paper if you quarter fold it. The latter is good if you want to enclose a printout with more information or a letter. The box of 100 envelopes costs a little over $10, and it lasts for a long time - unless you need to send out invitations / cards to a very large party, of course.