Appropriate behavior on a loved one's 70th birthday depends on the person and what kind of attention he wants. A 70th birthday is a milestone worthy of celebration, and a party is a suitable way to honor the person. How formal or casual the party should be depends on the guest of honor. If he doesn't want a party at all, treat the day like any other birthday, with a nice dinner out and small gifts.

Ask the celebrant whether he likes the idea of a party for his 70th birthday before you begin organizing one. If he says, "yes," discuss whether he would like a formal event or a casual get-together, then ask him to compile a list of invitees. If you think he might enjoy a surprise party, check with his closest family members to confirm that it's a good idea, and make sure he doesn't have a heart condition or other health problem that might be aggravated by a mild shock.

Organizing and setting up a party shouldn't be the responsibility of the guest of honor; you and any other party planners should take care of all the details. Consider renting a room in a restaurant or other venue. Or clear a space in your home, set up tables and decorations, and have the party catered. Unless the guest of honor has requested a casual party and you know he has an irreverent approach to aging, opt for a classic setup, including tablecloths, centerpieces, a bar for drinks and background music. A themed party celebrating the guest of honor's favorite hobby or the decade of his birth may also be appropriate.

For a small gathering, invite only close family members and longtime friends and business associates. If you can accommodate more people, widen the list to include extended family members and newer associates. It is appropriate and encouraged to invite people's significant others, but not mandatory if the guest of honor doesn't know them and you have limited space. Inviting children is optional as well, especially for a formal, evening party. If you choose not to invite them, add a phrase like, "We respectfully ask that the party be adults-only" at the bottom of the invitation. Also, include a mention of any dress code.

If you are invited to a 70th birthday party, RSVP promptly and be understanding if your significant other or children are not invited. If the dress code isn't specified in the invitation, call the party planner to inquire or deduce it from the formality of the invitation. A professionally printed invitation with an RSVP card and envelope included indicates a formal event, while an evite or Facebook invite suggest a more casual occasion. When you attend the party, keep your language polite and clean, and don't make crass or embarrassing jokes about the guest of honor's advancing age -- unless you know him well and are certain he will not be offended.

Unless the invitation says not to bring gifts, it is appropriate to do so. Suitable gifts might include a fine bottle of wine or spirits; vintage items dating from the guest of honor's childhood; records or photo compilations from the year he was born; or hobby items specific to the individual, such as jigsaw puzzles, elegant editions of favorite books or gardening tools designed for seniors. Avoid gifts that might be difficult for the recipient to use; at age 70, his eyesight, flexibility, strength or stamina may be weak. Unless you are certain that the guest of honor embraces his seniority with humor, choose a card that honors and celebrates him, rather than a humorous card that mocks his age.